This game is all about combinations of class units. If you play it on the mode that only lets have 1 of each unit, healing becomes very important. So every team you run should have at least 1 healer. The only sources of healing you have are from: Priestess (cheap single target heal & expensive AoE heal, both costs mana), Heretic (spammable semi-AoE heal attack that doesn't cost mana), Paladin (Tank single target heals), and Drow (weak single target heal that costs mana, and she's frail).

To get the most XP & money out of each dungeon, you want to keep exploring until the dungeon kicks you out. Going through a dungeon doesn't actually cost time. So you want to recruit as many units as possible to do multiple dungeon runs back to back. Each dungeon requires a party of 4, any extra units you have that weren't part of an adventure can be told to do missions. You want everyone to finish their rest and missions at the same time to give you the most options for choosing your party

The first two units are assigned melee roles, and the last two units are in ranged roles. Some units can do both roles, so you should try putting them in the front and trying putting them in the back to see which role they are better at. Ninjas have the option of jumping from the back to the front and from the front to the back, changing the 2nd unit's role. This can be quite good as it soaks damage, while also enabling the 2nd unit to change attacks

Building up a girl's affection is really important because it lets you have sex more frequently, which gains you mana faster. So in the beginning you want to take actions that convert lust into affection, which makes them open to bigger sex options, which builds affection and lust faster. Over time you also want to stack fetishes (from items you get in your adventures) because it makes them more open to different sex options, which makes it easier to increase affection and lust

Don't get the brothel, it's bugged, it loses you money even if you pay whores to join it