So you're trying to impress your new squeeze and it's her birthday. This is one day of the year that you can't mess up. Here is a fool-proof guide to impressing your girlfriend on her birthday.
Send her something! It doesn't matter if they are flowers, candy, a teddy bear, or all three! Send her something. Send it to her class, her workplace, or deliver it personally. Girls love when they get something from their Boo publicly. No one wants to be that girl that doesn't get something from her boyfriend (in front of all her girlfriends) on her birthday.
Leave her a note. Get up early and leave her a note in her car, or drop one in her locker. She'll eat it up. Taking extra time to do something special for her, shows her you care.
Be Original. Any guy can take his girl out to eat. If you want serious brownie points, cook for her. There are plenty of easy recipes on the internet that will make her putty in your hands. Even if you screw it up, nothing says "you care" more than attempting to cook for her.
Make her a gift. Again, anyone can buy an expensive gift. Some girls may appreciate an expensive gift, but not as much as something that you spent the time to make. Make a scrapbook of goofy pictures of the two of you. Depending on the sense of humor you share, maybe a nice macaroni necklace would suffice.