Dodging is the single most important skill to master in tide games.

The in-game tutorial really does not go over all of the things dodging does for you or how to really get the most out of it. all weapons have a "dodge limit" usually governed by the mobility or defences statistic. more dodges is always better. maximizing dodge count should always be a high priority.

Dodges take a second of not dodging to recharge, and dodging also halts your stamina regen for a second. when you run out of dodges you can still dodge, but they will be substantially less effective at actually moving you out of the way of danger, and will have considerably longer delay between each dodge. Consider getting "NumericUI" as this will show you your current dodge count so you can really see the difference when you're out of dodges and dodging into the negatives. At 100% +2 (so if you have 4 dodges, then at -6, or your 10th consecutive dodge) you cap out and your dodges just don't get any worse.

When you dodge enemy tracking is broken, and for many attacks you are effectively unhittable for a fraction of a second. This is called "dodge state". Enemies track you with their attacks. If an enemy has initiated any kind of attack directed at you, it WILL hit you, unless you initiate a dodge sometime between when the enemy commits to the attack "telegraphs it," and when the attack arrives. You cannot simply "step out of the way" of any enemy attack, it must be a dodge, or otherwise put you in dodge state.

You can extend dodges by crouching during the dodge, this will convert your dodge into a slide, and sliding makes you immune to ranged, but not melee. Slide dodging can also be used to "launch" yourself off of higher ground to go fast. Extending dodges this way costs and additional dodge. Slide dodging is also extremely useful for closing the distance to shooters of all kinds, turn yourself sideways to your target, and slide dodge towards them, evading their volley and getting you much closer to melee range.

"Spot dodging" occurs when you dodge into geometry (like a wall). the game considers you moving for the purposes of dodge state when this happens, even though you don't go anywhere, however some attacks can still catch you in this state (mauler/crusher overheads). Consider using the mod "keep dodging" so you can just hold down the dodge button to dodge as soon as the game will let you as fast as it will let you.

Most human size enemies are vulnerable to stagger from normal hits from any melee and especially being pushed, however bruisers have more hit mass and you may have trouble staggering a lot of them at once with a sweep and may need to push to reliably stagger them. Nurgle blessed (stinky) enemies have a green aura and will not stagger unless you have stagger boosting blessings or talents, or hit them with something special.
Hordes tend to file in as a trickle before they turn into a wall. This can be a problem since as you start hacking away at the first ones, stagger locking them with each strike, new ones can file in with their lunging attacks and interrupt your combo, causing you to suffer hit stuns, lose toughness, get hit by additional attacks because yours didn't go through to continue the stagger lock, and generally just eat ♥♥♥♥. It is important to keep an eye and an ear out for new additions to the pile of enemies, and make sure you hit them before they hit you, or push them with the rest of the crowd to get everyone on the same page again. Pay attention to the sound cues of incoming attacks and consider getting the mod “spidey sense” so you can have reliable visual indications of the alert sounds the game is SUPPOSED TO (but very frequently fails to) play to alert you to incoming attacks. Hordes want to surround you. Enemies to the left and right will happily go right around you and start hitting you in the back if you let them, it is therefore important to "manage" the horde by keeping it in a somewhat tidy shape through sweeps and pushes, making sure none of them slip by you to start hitting you in the side or back. this is extremely important as enemies to your side can physically block you, and if you suddenly need to dodge a trapper net and there's a poxie in your way, you are in for a bad time.
Pushing is incredibly important for everyone. it's not just for dogs and bursters, although it is absolutely vital for that. Pushing a group will cause all enemies in a 360 degree arc around you to be staggered, and give you time to wind up a nice heavy to cleave through them, initating your good stagger locking/horde management combo, or a little space to move and push again to shove your way out of a tight spot. please note that while most human size enemies are extremely vulnerable to pushes and heavy hits, muties, ragers, maulers, ogryns, and bosses will not really give a ♥♥♥♥ and you will need to dodge their attacks, maybe block, or potentially, use something special.
Maulers, ragers, and crushers are the big ticket melee threats and are pretty tough to engage with in honorable melee combat. Ragers are especially difficult to stun and will just combo you down, quickly eating through your block, stunning you and taking huge chunks out of your health. Maulers and crushers have powerful overhead attacks that cannot be blocked and can crush your entire health bar in one hit. It can be very tempting to just spam dodge when these guys are walking towards you, menacingly, but unless you have something you can pull out and nuke them down with from range before they get back within melee distance, you're just going to end up having to engage them in melee with no dodges or stamina.
If you can dodge far enough back you can absolutely disengage the enemy from melee, turn and sprint away to potentially gain more ground, or use something special to knock them down and retreat to a better position, but actually engaging melee elites in melee is going to require some very well timed dodging, and some moderately special equipment or talents or combos to hit them hard enough to get them staggered and under control. crushers especially have stagger immunity after being staggered, so try not to be out of dodges when they start winding up their overhead, wait for it to start coming down and dodge!
To be honest the best strategy for maulers, and ragers especially, is to just shoot them. I would not engage ragers in melee without knowing exactly how to use that weapon to stagger them, and even then only if i can fight them one at the time... or if i'm an ogryn.

Generally speaking you don't want to block. Blocking takes stamina, and blocking an attack with insufficient stamina will cause a hit stun. Pushing is generally preferred, but if the enemy cannot be pushed (maulers, ragers, crushers, bosses) and you're not able to get to a safe distance, blocking while you move can save your life. Reflect on the minor error that got you into that situation and move on with surviving.

If you cannot confidently dodge every attack, and you cannot reliably stagger the enemy, you should absolutely block them, even if that means eating the stun.

Blocking is omnidirectional but costs much more stamina to block attacks behind you, so try not to turn your back on things you need to block like ragers and bosses. Blocking also resets your combo. So if for example, you just wanted to throw heavy 1 on a weapon all day long, you can heavy attack, block for just a moment, repeat.

Holding the attack button after pushing does a push attack, push attacks are very often very good and worth doing, often even above a weapons normal moveset. You'll have to learn what each individual weapon's push attack is and when best to use it, different marks within the same category usually have different push attacks. Consider these a way to burn off excess stamina to get more value out of each moment of melee combat.

Special attacks on weapons are very unique and very situational, some offer a low damage attack that can be used in place of a push at 0 stamina, some offer exceptional stagger on headshot, some are activations that make your next attack much stronger, some are a special kind of hit that can make your combos more deadly, and devil's claws can parry.
Special attacks on a few weapons can stagger usually unstaggerable enemies. the default shovel special can stop a mutie in his tracks if you hit him in the head, ogryn bully club slaps can even stagger bosses to the weakpoint (sometimes, its complicated).

The way weapon combos choose which attack to use as you switch between lights, heavies, specials, and push attacks, is not always immediately clear or intuitive. So take the time to experiment and learn which light attack follows a special, which light or heavy follows a push attack, ect. For example, using the combat blades, a light attack after weapon special performs a downward stab with the same damage as a heavy. With ogryn's bully club mk 2, a light attack following a special performs a unique punch with good maniac damage, which is useless but kind of cool. Dueling sword's special comes out lightning quick and can be used immediately after a heavy to greatly increase your single target burst. With the chainsword, push attack chains to light 4. heavy sword specials greatly increase the speed of the heavy you follow it up with. The list goes on and on.
Using the best attack for the target(s) in front of you will greatly increase your combat effectiveness, so learning how combos work will be a strong component of mastering any weapon.

Toughness in darktide is similar to, but not quite the same as something like armor in payday 2, or shields in halo. while toughness will 100% protect your health from bullets by absorbing damage until depleted, melee damage is different.
Melee attacks will "bleed through" or "chip" your health based on your current % of max toughness.
Which is to say, at 100% toughness, toughness will absorb 100% of the melee hit and 0% will go through to your health. At 80% toughness, toughness will absorb 80% of the hit and the remaining 20% will go to your health.
It is therefore vital to keep your toughness at 100% as much as possible. you should consider being at 100% toughness as you having "one free ♥♥♥♥♥♥" where someone can bonk you consequence free, but after that you need to tighten up and refill before you start losing health to chip damage.

You are allowed to move and even sprint while charging a heavy, for most weapons this slows you down, but with a few weapons this actually speeds you up (daggers, dueling swords), charging a heavy with these to get the movement speed boost can then be extended by sliding, significantly improving your overall movespeed. Sliding a lot also helps conserve stamina, as sprinting only consumes stamina when you're actually sprinting, not sliding, and sprinting with stamina is significantly faster than sprinting without.

It is worth knowing what "kind" of armor each enemy has as this will affect your ability to kill them efficiently in melee (or at range). many enemies have several armor types (reapers and bulwarks are unyielding with a few carapace bits), but in general the breakdown goes like this:

unarmored: groaners, snipers, bombers, dregs (yellow dudes)
flak: scab (black dudes), maulers, shotgunners, bruisers, gunners
maniac: muties, flamers, trappers
infested: poxwalkers, dogs, bursters
carapace: crushers, and mauler helmets
unyielding: bulwarks, reapers, bosses

Curio selection is frustrating, everything about the gear crafting system is frustrating. but as with all things knowing what is good and what to aim for will help you get there as fast as possible.
Curios have one of 4 primary stats, Toughness, Health, Stamina, and Wounds.

Generally speaking toughness is going to be your best bet for any build, because of how toughness works, and the fact that most of your skills and kills restore % toughness, and almost all damage deals flat toughness, you gain a respectable advantage in combat by just simply having more toughness to work with.

Health can be a good option if you are making errors and suffering chip damage pretty regularly, but don't find yourself going down too often. i don't like to recommend health as it can put a strain on medipacks and it effectively betting on bad play but it is an option, especially for ogryn who would theoretically benefit the most from it.

Wounds are kind of bad. unless you're running the funny zealot woundmaxxing build you should not take wounds as a serious strategy. If you are still learning and still making major errors that are getting you killed alot on like malice and heresy then sure, take some wounds so you won't just flop dead before the next medicae station, but consider this training wheels, this is not a good way to play.

Stamina is very situational. if you're running deadshot on veteran stamina has some pretty formidable value, for everything else, not so much. If you're running a weapon with really bad stamina, like a knife, running a +3 stamina curio can make it feel much, much nicer to use. Or you can stack it for shield ogryn if you feel like being extremely silly.

Secondary stats seem complicated but there are definitely a few stand out options.

Revive speed (ally) is the best curio stat and you should have it on every curio you wear, in every build you run, unless you are explicitly planning on running true solo you will get incredible value out of being able to pick up, rescue from ledge, and un-net people in 30% less time. please note that this does NOT currently affect the speed at which you rescue people who have just respawned, for some reason. Go complain on the fatshark forums about this grievous oversight. Regardless, this is still the best curio secondary.

Corruption resistance is a pretty good pick as it helps you blunt the lingering effect of bursters, pogryns, poxies, daemonhosts, and grimoires, ideally you shouldn't be taking alot of damage from any of these things but nobody's perfect and this covers some situations you may have less control over than you'd like.

Toughness is also a good pick. it's not a lot but 5% toughness is 5% toughness and toughness is pretty good.

Extra Dockets is surprisingly useful once you're winning high tier missions and are in the business of pulling the lever on the Brunt's army slot machine until he gives you something usable. you can easily burn millions of dockets doing this.

additional chance of curio from mission rewards can help making the process of getting full sets of each kind of curio you want a little less painful, but becomes completely obsolete once you're happy with your curios.

Combat ability regeneration is kind of good, maybe to the point of being unethical, especially with the skill trees being how they are and cooldown reduction being so omnipresent and overpowered.

Health is ok but not as good as toughness and i would only take this if you were already stacking health for some reason.

Gunner resistance is probably the best option of all the enemy specific resistances just because ranged damage can be very oppressive if not dealt with quickly.

Sniper resistance can let you do a funny thing where you get enough toughness and toughness damage reduction to tank a sniper shot without losing health, but you really should not be getting hit by snipers, just dodge.

Extra experience is obviously only good when you're leveling up but completely useless when you're 30.

Toughness regeneration speed is surprisingly bad, it only applies to coherency regeneration and if coherency is your primary source of toughness you are doing something very wrong. completely useless when you are last man standing.

Stamina regeneration affects the rate at which stamina regenerates, but not the delay before it starts regenerating. This isn't particularly bad but you may find it a hard sell in your builds that aren't extremely stamina intensive like deadshot vet.

Sprint efficiency is generally made obsolete by just using good movetech and sliding everywhere

Block efficiency is generally not preferred, but has some use on non-ogryn classes when you end up needing to tank a chaos spawn and have to block some of it. a little goes a long way.

The rest of the enemy specific damage resistances are just not worth taking because you should be taking almost no damage from any of them in the first place.

typically there are a few blessings that are either completely transformative (brutal momentum/deathblow) or just better than the other blessings for any given weapon type, keep an eye out for these so you can always have them available.
You may notice a few blessings show up a lot on this list, for good reason.
To review: brutal momentum, slaughterer, uncanny strike, headtaker, and thrust are almost always must picks.
Deathblow and Brutal Momentum (Bromentum) are worth singling out because their effect of not only decent weakspot damage, but hit mass reduction has a MASSIVE effect on how many enemies you can cleave through and kill with each swing. more than any other blessing always try to have these blessings on weapons that can use them.
For perks, generally you should lean into whatever your weapon is already good at rather than trying to boost things it's always going to be bad at, e.g. carapace damage on devils claw is worthless. If you're not sure, flak is ALWAYS a good choice, maniac and crit chance are also usually good, but typically getting the right blessings is much more important than getting the right perks, but having both is definitely worth it.