I feel like when you're asking a girl to prom first you have to be confident and not afraid. Before you ask a girl give her sweet gestures throughout the day. Find out her favorite things (candy, sports, hobbies, etc.) and put them in her classroom or write cute little notes. So at the end of the day she is sweetened up and you ask her however you want to but just make sure there are flowers or chocolate. ( depends on who you want to ask) or if you are really close to her do something at her house. Like with her room or put candles on the drive way super late and have her come out and look. If not super close do something at school and make everyone jealous because you didn't ask them. Make it special! ( if you need specifics ill help you in class)