If it isn't GMed by a known quitter and if it's an idea I can get behind I'll prolly join it. 

Alternatively I'll join really mediocre stuff if I'm craving some mediocre stuff.

Also, if it's Yu-Gi-Oh!, there's about a 95% chance I'll join it no matter the quality.

EDIT: As to how I find it... I basically click on every single interest thread and look at the first few key words.