Psychologically, it's generally true that dark rooms appear smaller, while bright rooms appear larger. Light makes a room feel open, inviting and cheery. So, one of the simplest ways to make your dorm room look bigger is to add more light.
Natural light is best, of course. We assume your college won't let you bulldoze a wall to make an extra window for you, but if you have a window, take full advantage of it. This means that you should avoid covering it up with dark drapes.
Whether you have a window or not, you'll need artificial light, of course, but you shouldn't rely completely on a standard-issue florescent overhead light fixture. For a good effect, add a few lamps around the room for both ambient lighting and task lighting. Ambient refers to general lighting needs for the overall room, but task lighting illuminates a particular area, like a desk.
Of course, it also matters what the light will shine on once you have it in the room. The next tips have to do with maximizing your light as much as you can.