I have to say, the first thousand was hard, but I'm already at over 5k with 16 days to go until my next payment.
A few hints from my own pov (which is untainted by any guides, just based on my own play):
Do goblin dungeons. You should probably try to have at least one tank character (Seraphs make amazing front line tanks if you can snag one with decent stats) and a mage (I recommend "Scholar" for the early game since this brings healing to the table). If you have a fairy or an elf, you can get the "Druid" class which has a powerful crowd control attack that stays useful throughout the run.
Anyway, do your dungeons when you can. Use daisy for prostitution as she's practically designed for that specific use. I generally use my free slave from the beginning to cook meat soups and fish cakes (my master character is a halfkin cat, so he loves that). Meat soups are great for two reasons: 1. Almost everyone loves them, and 2. You get three food for the price of two!
In order to get a bit ahead, I started purchasing ALL the meat and vegetables that the shop provides. I convert it all to meat soups, then sell the majority of them back. I spend 5 gold to make 3 meat soups, which then sell for a total of 9 gold, almost doubling my money every time. This adds up over time.
Make sure that you have room when you start going after bandits. You can capture and sell the leaders at the end for a little bit of extra money on top of whatever else you get just from running the dungeon. Usually around 2-300 gold for them.
If you have extra resources and a character who is good at it, use your forge to craft high powered items to sell back. The resources and time are well worth the 300+ you'll get off of decent quality items.