I figured out the efficiency tips below by myself during my first playthrough, and by using them on my second playthrough, I got a platinum trophy, with $1 million revenue and 61k fans. On my third playthrough, I got diamond trophy with $28 million total revenue and 318k fans. Proof.[prntscr.com] Edit: it is worth nothing that since I wrote this guide, the game has been rebalanced to be harder, and thus the image is not representative of the current state of the game.

These tips are in no particular order of importance.

- Hire a girl with 1 Style and 1 Talent to be your designated errand girl. Use her to fetch licquor and cigarettes from the store, hire new girls, and earn items from the Adult Shop. This frees every other girl to earn money 24/7. Equip her with the Shopping Basket item, which doubles the amount of licquor and cigs she fetches.
(Note: in emergency situations, don't be afraid to use all your other girls to get booze & cigs fast. It's better than letting those get to 0 stock).

- To give an item to the girl, drag the item from the Books tab to the girl's portrait on the right side of the screen. Beware that once given, items cannot be recovered back to your inventory; only destroyed. A girl cannot equip two of the same item.

- Buy the "collect from the buildings every 15 mins" upgrade as soon as you can. It is extremely cheap and saves you a lot of time in the long run from not having to collect money, licquor, cigarettes, talent points and style points yourself!

- Fans a girl earns are split equally between her fetishes. So if she earns 60 fans while having three fetishes, each fetish will gain 20 fans, which in turn increases the fan count of any girl sharing that same fetish. With this in mind, try to hire girls with the same fetishes as much as possible. Not only it gives them a valuable boost to INITIAL fans, but they share newly earned fans between each other, like in a massive, delicious gangbang. Hnnnggggg.

- When you "accelerate time" by clicking a building with girls inside, it will accelerate time for ALL girls inside by the same amount. As such, you should always strive to put your girls all on the same task at any given time, rather than spreading them around. This maximizes the effect of your time acceleration. So, whenever one girl has to use the spa (rest), try to put all the other girls there too, even if they are not particularly tired.

- Spamming click accelerates time faster than holding click. Whether it's worth the finger cramps is up to you.

- Don't forget to check the promos every day and buy them. Make it a habit to check the promos as soon as you hear the midnight bell (Ivan Pavlov would be proud of you!).
Initially, buy only promos for the fetishes your girls have. In the middle to late game when you're making tons of dosh, buy them all every day!

- My favorite items are the Piggy Bank and Subscribe Pillow. The former cuts salaries in half, which helps a lot in the early game, when salaries impact a lot on your finances. The latter gives girls fans when they cam, half the amount they would have earned if they had used the photo studio instead. It makes the photo studio obsolete, and is highly recommended for all girls (except the errand girl of course). In fact, it is probably the single best item in the game. Prioritize it above all other items.
(Pro tip: give the Piggy Bank to the most expensive girls first).
(Note: much more effective strategies regarding these 2 items have been found since I wrote the above. Because they're almost game-breaking, I have added them to the next section of this guide).

- Whenever the Adult Shop is not offering the above 2 items, try to get always the same sex toy and equip it on all your girls later on so that they share yet another fetish. Or even better: if there's a fetish that suddenly has a crap ton of fans due to promos, get a sex toy for that!

- Using the girls as escorts is not worth the risk. The probability to acquire an STD is way too high, and curing STDs is too much of a hassle (the cure is obtained from the Adult Shop, takes 3 days to act, and uses up an item slot for that duration). It would be worth it if the Condom item didn't last for only a single use (seriously, devs?). Plus, the girl can get AIDS, which makes her unable to do ANYTHING AT ALL and is incurable, effectively killing her for the rest of the game (you can still substitute her for a new girl, though, by dragging another girl from the roster in the first tab to the AIDS girl's portrait on the side bar).

- User SolacelInfinitus adds: "One thing I highly recommend is to avoid smokers and drinkers entirely. I'd rather get a girl with a decent fanbase and no addictions, and invest the time into getting her skills up, than either have to constantly have my errand girl buying cigs and liquor or waste a valuable item slot on a nicotine patch or wine box."

If you have more tips, feel free to comment and I'll add them giving credit to you.

I applied the above tips in both my second and third playthroughs, but on the second I got $1 million revenue while in the third I got $28 million revenue. "Why the huge difference!", you're thinking. That's because I used a few new tricks.

WARNING: reading this section will completely spoil how to get a diamond trophy, which robs you of the enjoyment of getting there on your own two feet. Are you really sure you want to read it?

First, I learned something very useful about how you fail in this game. If midnight strikes and your finances go in the red, the tutorial girl will beetch at you about how that can't happen again in 24 hours. Turns out, she wasn't very clear. Midnight can't strike again with your finances in the red, but if they are positive when midnight strikes, even if it goes red again, you won't fail. This allowed me to overspend on upgrades without worry. You'd have to make a veritable effort to lose in this game!

Second, I tried a different tactic in the early game. Rather than just camming a lot with the first girl, I quickly hired 2 more girls by camming a little bit and then spent a whole day making them do photos instead. I discovered that this early fan boost greatly increases your profits from camming so much that it more than compensates the day you spent not camming. In fact, rather than reaching the 3rd day with $250 revenue, I reached it with almost $500 revenue with this tactic!
At some point I used ALL the girls on the Adult Shop to try and equip everyone with Subscribe Pillows ASAP. Once that was taken care of, I forgot about the photo studio for the rest of the game and just cammed. I used the errand girl to stock up on 3 extra pillows to ensure I had them right away as I hired new girls.

Third and most important, I realized that salaries don't hurt your progression/finances nearly as much in the late game than they do in the early game. I decided that I would ditch the Piggy Bank at some point. Thus, I started stocking up on sex toys for popular fetishes early on.
I had already given each girl water bottles as their 3rd item so that they'd share the water sports fetish. At some point I noticed that the furry fetish was rising, so I started giving cat ears to the girls in place of the piggy. Due to the randomness of promos, though, by around day 16 the bondage fetish had massively climbed ahead of both furry and water sports (but furry still had more fans than water sports). So I started substituting the water bottles for mouth gags.
I think this was the main factor that made the third playthrough so superior!

Finally, as per SolaceInfinitus' suggestion, I made it a point to hire the girls that don't smoke or drink (or only sometimes), even if they start out with low talent & style. As it turns out, this greatly freed up my errand girl to get a lot more fetish items than she otherwise would have been able to, and took a burden off my mind by not having to watch booze & cigs as much.

User Slashley points out that the fan gain from the Subscribe Pillow becomes completely irrelevant in the middle-to-late game, because even if your 8 girls have pillows and your "fan gain from photo shoots" upgrade is at maximum, you'll only be gaining around 500 fans a day in total. This is much less fans than a single promo gives at that stage of the game. Thus, it's much better to replace the pillow for a fetish item as soon as your fan gain from promos starts to greatly outperform your fan gains from pillowing.

Slashley also found out that the number of fans promos give is based on your current fans, and caps off when you have 100k fans, at which point the promos can give between 5000-9999 fans each, randomly. As such, one should strive to reach 100k fans as soon as possible, and from then on, RNG will determine your final results, as you'll be earning anywhere between 40k and 80k fans per day. Here's him proving you can get 600k fans this way.

TL;DR: A balance of both.

Here's a comparison, assuming 200 initial fans for the girl, and fan gain only by camming with the Subscribe Pillow (which, remember, gives HALF the fans from photo shoots).

Talent lvl 1: earns 0.5 cash per fan when camming
Talent lvl 2: earns 0.75 cash per fan when camming
Talent lvl 3: earns 1 cash per fan when camming
Talent lvl 4: earns 1.25 cash per fan when camming
Talent lvl 5: earns 1.5 cash per fan when camming

Style lvl 1: Earns 5 fans per photo shoot
Style lvl 2: Earns 12 fans per photo shoot
Style lvl 3: Earns 21 fans per photo shoot
Style lvl 4: Earns 32 fans per photo shoot
Style lvl 5: Earns 45 fans per photo shoot

Talent lvl 5, Style lvl 1: she'll have 200 fans on her first cam, 202.5 on the second, 205 on the third, 207.5 on the fourth... so she'll earn 300 cash on her first cam, 303.75 on the second, 307.5 on the third, 311.25 on the fourth...
By the 21th cam she's earning 375 cash, by the 51th cam, 487 cash, and by the 101th cam, 675 cash

Talent lvl 1, Style lvl 5: she'll have 200 fans on her first cam, 222.5 on the second, 245 on the third, 267.5 on the fourth... so she'll earn 100 cash on her first cam, 111.25 on the second, 122.5 on the third, 133.75 on the fourth...
By the 21th cam she's earning 325 cash, by the 51th cam, 662 cash, and by the 101th cam, 1225 cash

Talent lvl 3, Style lvl 3: she'll have 200 fans on her first cam, 210.5 on her second, 221 on her third, 231.5 on her fourth... so she'll earn 200 cash on the first cam, 210.5 on the second, 221 on the third, 231.5 on the fourth...
By the 21th cam she's earning 410 cash, by the 51th cam, 725 cash, and by the 101th cam, 1250 cash

As you can see, a balance of talent and style seems to be better both for medium term and long term gain. Of course, I'm not considering the fan gains from promos and shared fanbases between fetishes, so as soon as you start getting the vast majority of your fans from promos (should happen in mid-game), prioritize talent! By this point, style will become obsolete.