Make friends with your teachers. To get on their good side, read the material before class, ask questions, and use their office hours to get clarifications on material that's unclear.Read the whole thing here.
Learn to manage your time. Make sure you do your work on time (and neatly) and follow the instructions carefully on assignments.
Be well rounded - take classes in the area you want to specialize inm, but also in others. You never know what you might end up using, so it's important to have both depth and breadth of knowledge.
Affability and netness count. Join a frat or sorority, or some other group. And if you dress like a slob, make sure your thoghts and speech are more ordered - it'll offset the impression your appearnace makes.
Finally, don't indulge to excess, get some exercise, and develop good work habits.
As a professor, I can vouch for the first piece of advice. Most students don't make the effort to get to know me outside of class. So, I tend to go the extra mile for those who do (particularly when they need reference letters).