Aaah, so many people feel just like you do - don't worry! I'm just about the worst person to ask about relationships, but this is my two pennies worth:
1. Don't feel that she is out of your league!
2. Try to be relatively outgoing
3. Make jokes! (only if they're funny though hehe)
4. Smile - people subconsciously find you more attractive if you look happy
5. Don't try too hard - you'll just put girls off
6. Act or be interested in her and her life - don't just talk about yourself, but equally don't make your conversations seem like question and answer sessions!
7. Try and seem confident but not arrogant
8. Take pride in your appearance - even just having a great haircut can make you feel ten times more confident and will be a talking point when people notice the difference
9. Don't ever criticise her friends
10. Make sure she knows that you're single!
11. Girls don't always like guys that seem 'nice', try and be a bit cocky - most girls find this attractive, at first at least - very grounding!
You probably know all this already, and in some ways the best advice I could give is to just be yourself - that's the best anyone can do!
Hope things work out for you x x x