The pictures only really look good because I make a ton of them and pick the best ones, but I can probably give a bit of advice.
I find that simple prompts tend to work better, use plain words over slang, like I find that "Breasts" works better than Boobs or Tits when making boob focused images.
If you're making images of an existing character (like a Pokemon) try putting just their name in first to see how the AI recognizes it, after that you can add other prompts to fine tune it into what you want.
I hope that you do have a go at making a game, I'll be happy to give any writing/coding advice if you need it!