There’s quite a few factors. First, I check for any organization. A good roleplay and a well thought-out story will have some sort of organization skills. Next is the story and genre. Particularly, I’m more into action and adventure, but it’s a good thing to take notice to. Another idea is looking at the characters. Are there too few of this kind or too many of that kind? There should be a diversity of characters. Too many of the same kind of character can kill an RP quickly. It took time to take notice to these things, but after a few years of joining RP’s, it definitely helped.