Being well-mannered doesn't mean you're boring — it means you know how to treat other people with respect, a quality most girls want in their boyfriends. Show her you know how to be considerate by doing these things for everyone, not just her:
>>Say 'please', 'thank you' and 'you're welcome.' As well as asking with a 'I'd appreciate it if' or 'I would like for you...'
>>If someone is walking through a door behind you, hold it open for him or her.
>>Avoid cursing or saying anything crude in public, or in mixed company. It's fine to relax a little around your friends, but try to show your best side around people you don't know well.