There are 3 rules to asking somebody to dance:
Rule 1: Make Eye Contact
If eyes are the windows to the soul, then eye contact is the doorway to asking somebody to dance. If you can't make eye contact with a person (because they're deep in a conversation with somebody else, playing with their phone, or walking briskly past you), it's probably best to ask somebody else. If you're behind them, tap them on the shoulder or walk around them. Once you have eye contact, you're all set to proceed to rule 2.
Rule 2: Smile
Pretty straightforward and it makes a great first impression. It's the best way to show to a potential partner that you're excited about dancing with them!
Rule 3: Actually Ask
You have to actually ask out loud. Just sticking out your hand and waggling your eyebrows suggestively doesn't look nearly as cool as you think it does. This is especially important because it gives our partners a chance to say 'no'.
If you ask somebody and they say no, don't take it personally. It's not a big deal. There are tons of other people who'd love to dance with you, so go ask one of them!
by Paul Mandel