I just think of my RP level judged by myself and harmonize it with my current situation. Say... I am good enough to RP in Casual or Free, but not Advanced. I could go for Casual, but if I don't feel like it/ have the time/ etc I settle for Free. But sometimes it doesn't matter as long as it interests me.
Done?Well then I search for a criteria to search it by, like... do I want a 1x1 with a story, just another Arena fight-to-the-death? Maybe just a group RP, and if the latter then what am I expecting? Say... a tournament, saving a certain person, object, place etc , for it to be post-apocalyptic, pre-apocalyptic. Violent or not, you know... you don't need to perfectly create a plot in your mind and(since it's also useless since different people think differently and there are bound to be differences even in the slightest) hope for it to be identical.
Ah yes, if there is a certain book, TV show, anime, manga which's universe you wish it to take place in or at least which you wish it to be based on, then that may also help.
At least... that is pretty much how I search for RPs, hope this helps.