How to tell if it's worth asking someone out?

Like, is there a certain period of time, a certain type of personality, a way to tell if they'd be even somewhat interested? People say "just ask" but I think that's stupid. If I end up creeping someone out, probably like 5 more people are gonna be creeped out by me too. Who knows how much further that could spread.

To help get a good answer, I'm not very attractive at all. Like, 4/10 probably. I'm in high school. I'm 18. I have no friends.

How to tell if it's worth asking someone out?
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