I am a native English speaker. I've noticed that there seem to be very strong rules about when to use contractions, but I haven't seen these rules enumerated anywhere. For instance, I think nearly every native speaker would say this is wrong.
"Who's going to the movies?" "I'm".
But is there a rule that you can't have a one word sentence be a contraction? No. E.g.
"What's your best advice on whether I get insurance from FlyByNite.com?" "Don't"
There seem to be quite a few of these rules. Are they listed somewhere?