Flirt: When she swipes your card tell her to swipe it again. When she does swipe it again start to giggle. Laugh louder and louder each time you hear the beeping noise. Yell things like "Don't stop!" or "Faster!" until someone comes to quiet you.
Ask her if she wants anything: She'll probably say no, but you'll be the first guy ever to ask the girl swiping cards if she wants anything from the hot-bar. She'll think you're suave, quirky and funny. If she's really into you she might ask for something sexual like a banana. If she does that you can skip the rest of these steps and just try to kiss her.
Eat with her: Carry your tray over to her little desk and pull up a chair. This shouldn't feel weird, there's no need to be uncomfortable around your girlfriend. Just remember to be polite, don't use your fingers and chew with your mouth closed. If she seems into this, now is the time to make a frantic grab at her boobs.
Hang out until the dining hall empties: Once no one is around just lie down on your back across a table and ask, "Now what do you want to do?" This is the part where she mounts you. Then the table breaks. But pay no attention, just roll onto the floor and let it happen.
Buy a lot of pop-tarts at the school store: You can never return to the dining hall again.