The main thing is to remember that the best gifts come from the heart and don't always have to be the really expensive, lavish monstrocities some people give. If you are a decent writer, maybe write her a poem explaining your feelings for her. Take her out to a nice dinner and have a deep conversation with her. Look into her eyes, grab her hands, and sincerely tell her you love her and wish her the best birthday ever....
....Or you could always buy her a diamond ring.
