First off I'd say avoid viewing all girls like potential girlfriends, view them as people you will meet and interact with.
Chances are you'll be standing in about 10 queue's for registration so chances are you'll be around people who will be in your department for a fair chunk of the day so just say "Hi, I'm Renegade-pizza. What are you here for?" Even test it on a few guys first, try generic and get to know people stuff. Avoid the weather and stuff, it always sounds like you are grasping at straws if it isn't some kind of fairly extreme conditions.
One thing that can catch you is if you have a nickname that everyone has used for years, like I did, I didn't notice when people said stuff but called me by my name. Seriously only my family actually used my name for like 12 years so people saying "Hey, Manythings!" passed right over my head for a shamefully long time. Probably a good idea to learn other people's names, which I really don't but I am very good at dodging around by saying things that could be applied to most people.
I would say if you really are hopeless at women (as many of us are) then don't try to be a pick-up line guy. Just don't. It works for some guys because they are either good looking or are very good at saying the right things in the right way. If you aren't either of those you sound like a tool. Talk to them and if possible try to work on your sense of humour hard. Making women laugh does work. Seriously keep in well order, I'm a notorious lazy shaver. Once a week give or take and I end up looking like a scraggly hobo but if there is a woman I at least try to keep it too once every 2 days.
I might add something elsse if I think of it.
JWRosser said:
Get a wingman to go up to them and go "Hi, haaaaave you met [insert your name here]". Then he leaves, and you're done.
On a more serious note, just be yourself. Comment on what she's doing (in an appropriate manor) or where you are, or if you're in the same class you can talk about that.
I would test this out in a controlled setting with a wingman you know you can trust rather than out on campus or whatever. Like a party or a club. (How I met your mother is a great show but I wouldn't call Barney a good source for tactics and advice.)