I'm a junior this year so I moved into a house off campus and thus have yet to eat at our cafeteria, which is an all-you-can eat buffet as well. My first two years of school I was eating there just about every day though! Here are some tips that helped me not pack on the extra pounds:
-sitting far away or not facing the food. If you see it, you're going to want it.
-make a salad first. filling up on fiber-rich veggies keeps me from wanting carbs like pizza and pasta.
-drink a glass of water before you head back for more food. sometimes real thirst is confused for hunger.
-the dessert station is definitely the highlight of our school's cafeteria, they must have at least 10+ things everyday. I'd opt for the choices that had fruit, like vanilla pudding with banana slices on top.