Think of your exercise schedule like a 1 hour class that meets three times a week. If you miss that class too often, you won’t know the material, and your professor could lower you grade even further than the resulting poor test scores. If you don’t exercise, expect to avoid the Freshmen Ten is as certain as an increase in tuition.
Aim for one hour, three times a week of cardio exercise. This means you should breathe heavily (almost as heavily as your roommate’s annoying sleep breathing). Walk, run, play tennis, or chase campus squirrels, it doesn’t matter as long as you get your heart rate up.
To really keep those extra pounds away (and attract some campus hotties in the process), try to do 30 minutes of strength training twice a week. Most colleges and universities have fitness centers. Ask to have a student worker or trainer show you the ropes and give you a good routine.