I've learnt the hard way with some of these. So this will hopefully spare new players making the same mistakes.

1. Don't use gems (the currency ones, not the socket ones) to buy gold, it is expensive and the exchange rate is ridiculous. 5 gems for 2,500 gold or 50 gems for 25,000 gold. That gold might sound like a lot to a new player, but when you start crafting and have unique and set items that cost in excess of 250,000 gold to craft that exchange rate very quickly shows how badly you are hurting your gem stockpile.

2. Don't waste resources crafting until you are ready to go beyond the campaign and do PvP and Trials. You will find plenty of equipment while playing the campaign and your equipment level quickly falls below par when your level (and that of the enemy) grows beyond it, so crafting at lower than level 70 is not advisable when you could be stockpiling resources for the good stuff.

3. Try not to use gems (currency kind) in "A New Beginning" unless you are certain you can meet the deadline and complete the various tasks or you lose gems and gain absolutely nothing. It is only viable if you can complete before the deadline and complete the tasks to gain rewards as well as reach champion levels to import to your main hero after the event ends. Avoid crafting if you can help it, because everything you use (resources etc) is less to transfer to your main character and you also lose any equipment if it is not transformed to Celestial.

4. Don't sell gems. Hoard them. They are used in crafting and socket items. Try to get 1 'page' dedicated to the gems in your storage. Ranging from smallest to largest. As later you can forge them into larger gems which have higher potency than the other gems lower on the rank.

5. Personally I don't make a lot of use out of jewellry crafting early game as it is expensive and the end product is usually not what you want stat wise if you use the random option. Getting specific stats you want can be expensive.

6. Once you have enough resources, craft XP % increasing gear to use in Trials. Go as far as you can to get the most XP you can, not to compete. Champion levels have a lot of added points to put into various sections (haste, power, critical rating etc) the sooner you max out these (apart from power, as power has no cap) the more powerful you will be and the better equipped you will be to get further into the Trials and PvP arena.

7. Once you have enough resources, craft gold % increasing gear so you can start earning gold in decent amounts. Gold is used all over the place in the game as a secondary currency and you will need A LOT of it.

Why I said to do XP and gold % increasing gear separately is because if you are using a slot each for both gold and XP, you are losing out on something more valuable like armour, vitality, power etc which will reduce how far you can get in a trial, thereby your XP gain per run. (no one wants to do a trial 100 times for 1 level!)

8. Avoid the PvP arena initially until you have at least epic level gear. If you do want to try it regardless try to pick opponents equal to or lower than your level. Any hero higher than yours and with better gear usually ends with a resounding defeat.

9. Try to save gems for the legendary crafter's crate. You are really going to need those resources to craft legendary level gear. Getting the XP 200% and gold boost 200% is also a good idea and will stack with your XP, gold farming gear.

10. Never open loot chests that ask for gems to unlock. They are NOT worth it. (this has been said many other places around the forums and web searches and I can in all honesty say I opened some and regretted it. The gems lost and gear, gold, resources gained are of VERY poor exchange rate when you consider you can buy a crafter pack and more likely get a better weapon, armour or craft the unique resource for a better price. (Not to mention crafting your own things gives you crafter's XP which has a set of perks that are vital for getting good stats on weapons, armour etc).

11. 1 Slot to increase your ability, passive and powers is enough. Don't waste 400 gems unlocking a second and (unknown amount for 3rd, as I never unlocked second) third slot. It is a huge waste of gems. Sure, it means faster ability upgrade, but unless you are forking out real money to buy gems, those gems you used could have been put to better use. Like crafting components and crafting.

12. Be patient. Don't rush your ability, powers and passives upgrades too far as they become really expensive on gems, initially the ratios are good. Personally I never went further than 25 gems per ability, power or passive. If you really haven't got the patience to wait for skills to level up on timers you will have to pay real money to get gems so you can speed level your abilities etc.

Both 11 and 12 take time and patience. If you are in short supply of either, you will be forking out hard cash. I'm not totally against this, as the developer should be supported. They have done a decent job of trying to balance making some funding for themselves and also giving players a way to grind and earn a sort of free way to do things.

13. Avoid unlocking more inventory space on your hero than you need. Personally I only unlocked 2 additional lines as that was all that was needed to finish a single run on campaign or trial without even having my inventory half full (that was with gold/gem boosting consumable.)

14. Similar to 13, avoid unlocking more storage space than you need. Personally I have 1 'page' of storage dedicated to gems and the other to armour. The second 'page' is dedicated to armour and fits 2 complete sets and accessories snugly with the 3rd being on my hero.

15. Build synergy with your hero. This is important for PvP and Trials. Only you can decide what will work for you, the trick is finding it. Some skills, abilities etc work in unison with certain armour, weapons. So finding that powerhouse build is quite a challenge and needs focus and thought.

16. Think about what you are doing, plan your crafting. Salvage equipment you don't want or need. Resources for crafting are a precious commodity and when you get to the legendary level of crafting those resources become hard to come by if you are crafting willy nilly. The important thing to remember is your resources will almost never be enough, because you will always have to craft gear with better stats and a higher level to push that bit further into the PvP arena or Trials. Waste not want not.

17. Avoid transmuting/crafting essences directly unless you really have to. If you have a good stock of lesser, the game will automatically show you if you are lacking a certain component and allow you to craft the needed amount specifically to craft the item you want. It is a simple case of what you need rather than just going overboard and potentially wasting gold on crafting more than you need or even converting one type of essence into another needlessly (which is the most expensive).

18. Don't sell epic or legendary items to Mitzu. He is cheating you blind. +- 1,500 Gold is all you get when to craft that same level gear can cost upwards of 250,000 gold! Salvage that gear (if you don't need it), you will get far more use out of the resources they give to craft your own gear.

19. Avoid buying weapons or armour from the blacksmith. You get more than enough throughout the game. Farming gear is your friend. Play with your friend!

20. Have fun. The most important tip I can give new players. I've likely forgotten a few things over the long period of bumping my own head, so this is not a comprehensive tip guide and I'm also not all knowing pro on the game.
If anyone has something to say or add to in the comments then feel free to share!
This game can become pretty addictive if you are into this sort of game. I wish you the best of luck and fortune on your journey.

Thank you for reading!