TLDR: Sleep outside the tavern if you have 40+ food. You're wasting money!
Also wash until -100 stamina for easy exp.
I have found the easiest way to make money early on is dancing at the bar. Only wear pants. You'll probably want exhibitionist trait so that Lona won't constantly be depressed. Every time they ask you to strip, do so and then put her pants back on and save. If you get hit by a bottle or whatever then reload. You can also allow them to cum on Lona if you don't mind it (it will help with tips and Lona's sex stats without any penetration). Just don't let them cum more than twice as Lona's stamina will probably run too low, and always just refuse and reload if they ask her to masturbate (say yes and you lose a LOT of stamina, say no and they get angry ~ lose/lose). They always ask you to just strip though if Lona is wearing her pants.
If you start with 65+ stamina then you should be fine if you only stripped. Anything less is iffy, but possible at 50 or so (ymmv). When the coins and crosshairs stop appearing then wait until the timer is almost done and save your game. This is very important. After the dialogue and you get paid, you'll either need to try running to the left or down, depending on the loiters. Either way you'll need to make your way upstairs. The adventurer with whip is the worst of the lot (despite having 50 morality he is the most rapey guy there).
If you're particularly clever you could trick a guy into grabbing at another one (wait until he grabs at you, then lead the other guy into it) and they will start fighting and take attention off of you. Don't hit them! You can use arrow keys to try and escape but any attack will lower your morality. Temporarily it will be like -160, but once you leave it will take a permanent hit. Always just dodge the patrons and go upstairs.
Now, it's important to note your food. If it's 10 or less then buy a key. As others have noted, you'll need to use 4 coins and buy a beer with the extra - which is good for Lona's mood (drink it or lose it). If Lona's food is 70 then you don't need to use a key. This is a waste of money! After you dance just save, leave the bar, and then press the ctrl key until the day ends. You'll sleep for free! You might get an encounter with guards but it's of no danger to Lona with good morality. You won't have as much stamina but you got to sleep for free and can dance again. It's a great deal! You can also do this again at 40 food. Again your stamina will be reduced, but it's a small price to pay for free sleep. This way you can dance 3 times a day in exchange for one key / 4 coins.
Once you save up enough money you should go to the street vendors just 2 blocks over and buy the glasses. Always wear them when selling coins and buying a key, and now you will only pay 3 coins per key.
I've saved up enough money to buy the complete golden outfit (that only prostitutes can wear). It seems effective for prostituting Lona in higher class areas, but the pay still isn't that great. As it stands currently, dancing is the best way to make money as far as I can tell. I really feel like prostitution should pay AT LEAST one small coin. It doesn't make sense that random guys would pay Lona with barter points (and unrealistic). If what she offers is not worth at least one coin then I feel the client should refuse her. The barter points system should only be used where appropriate (like with vendors). It doesn't make sense to use it for everything. Especially sex encounters.
Another way to make money, and a much better use for the golden sexy outfit, is to appear very weak and sexy at the bar. The key to doing this properly is to wear Lona's normal clothes then go up to the bar lady, change clothes, wait for some guys to start grabbing at Lona, then switch clothes back. They will de-aggro Lona now, but the Lady Boss will be mad and try to kill the bar patrons. Just stand aside and watch the carnage! Be prepared to pick up coins when they drop, and save your game after you get anything good. The guy with whip can drop his whip, bag, and shirt (maybe other clothing too). Other patrons tend to drop mostly the small coins, as well as random food items. Some can even drop the large copper coins, which is a real treat! If you care about the NPCs to the left (the girl and big guy) then exit if Lady Boss ever gets in a fight with them (they can usually deal with the other patrons). This happens pretty often when you're doing this, and the girl gets killed easy. IF, however, you don't care about them then let the girl get killed and pick up her swords. If you don't get 2 swords then you're getting ripped off so reload. Those swords are worth 4000 each! The big can drop a shield worth 2000. I think it's worth more to keep them alive (namely the girl, as she kills patrons quickly.. the big guy is stupid slow).
Final tip, when you have 10 food, 10 stamina, and they key so you can sleep.. don't! It's time to level up! See that bucket? Wash up. Wash again.. and again.. and again. Washing will give Lona free experience. I'm not sure if it varies based on level or what, but it's the best way to level up as far as I am aware (that doesn't involve being brutally beaten while starving and climaxing constantly thanks to weird mods). Wash all the way to -100 stamina and Lona will automatically sleep in the bed after that. When you want to sleep outside you could also go into a street, find a corner and wash until Lona passes out.. but this is more dangerous and Lona's stamina will be bad when she wakes up (possibly negative).
Edit: Forgot to note that all raw food will disappear if you exit any area, if you're playing Hardcore mode. (I suggest turning it off at the start, and if you wait and turn it on/off later then you'll get a sex trait that says you abandoned hardcore.. dunno about you but that page is cluttered enough as it is. lol).
The best way I've noticed of getting GOOD food, is getting the Lady Boss at the tavern to kill her patrons (as I mentioned earlier). The patrons will sometimes drop rations and sausages, which both will keep indefinitely. The sausages are best as they give 32 food each! Rations suck by comparison, so trade up for more sausages when you can, and save them for long trips and quests of importance. If you go gathering herbs in the forest later (the glasses help a lot), then I suggest a few points in survival for the free food, BUT you will also need omnivore so that all the fruit won't cause Lona to puke her guts out (so annoying...). This will prevent you from taking the tough trait, so decide which is more important.. being tough or being able to eat. lol (I think it's better to eat than be tough and starve to death, but that's just me)