Whatever you want. That's the thing. Most people don't bother that much with dressing up, but they don't completely phone it in either. Casual - cute is the thing most people go for. And when it's exam time - it's way more casual than cute.
There was this one girl who always came to college in extremely high heels, all made up, in skirts and fancy tops. I thought she was always going out rather than going to classes.
Don't go too fancy and don't go too casual - no sweatpants. O. o