>>938963375
Sort civitai by most downloaded or most liked and choose one, but most of them will get you good results. As for sampler, euler a is popular, I like dpm++ 2m karras, and ddim was popular for a while early on, but test them out and see what you like.

Sampling steps is up to you, but most people are probably in the range of 15-30 or so for the base gen and roughly 10-15 for the upscale, but you can worry about that later.

Illustrious works best at CFG 4-6, though you can try going more or less, but you can get over saturated images if too high and washed out images if too low.

As for prompting there are some model specific tags that you should use, but other than that get your tags from danbooru, or install the tag autocomplete extension.