I look for a question that is "unusual" in some respect, one that goes beyond a mere FAQ and requires more than a link to a prior thread or a perldoc page. That doesn't mean that I might not think about FPing a post that is incredibly stupid but has received some outstanding replies that are ingenious in how they point that out. :)

That said, if a question that would otherwise be thought of as run-of-the mill has generated some especially thoughtful answers I will FP it. But overall, I rarely FP something myself, relying instead on the judgement of other, more experienced monks than myself to do so.