First thing you do is get a flower, or a rose or something, Hide it behind you (Stick it in your belt or something similar to that)
As mentioned before make sure you smell good, and are on your best appearance.
Complement her, have a small conversation or something.
You then proceed to tell her that you like her, and that you'd be honored if she would accept to go out with you. You then summon the rose, and hand it to her.
Then she'll run away and you'll never see her again...
or maybe she'll accept and you'll live happily ever after... for a while.
Good luck, buddy!