[Question] How to "clean up" images?

Hi there, I've been toying around with Stable Diffusion for some time now and I'm starting to get a bit of a feel for it. So far, I'm quite happy with my workflow for generating image compositions (i.e. getting the characters, items, poses, .... that I want). But these images look quite crude sometimes. Question is - what tools can I use to iron out images, get them more crisp looking and so on, while keeping the image composition the same all the time? Any tips are highly welcome