Make fitness part of your routine
The number one concept to keep in mind is doing something active everyday. If you can stick to this, that's half the battle. Aim for at least an hour but it doesn't have to be all at once: 10 minutes here, 30 minutes there, etc.
If you like to be alone for your workout so you can focus on the task-at-hand or just focus on your thoughts then going to the gym in the morning or taking up something such as cycling or running may be for you. This can be especially rewarding for those of you who have very socially-geared classes or a coop placement.
If you are the opposite and prefer a social environment, then I would suggest fitness classes or a running group. If you go regularly, you'll find it much easier to meet people with common interests. The added bonus is that these workouts are generally an hour long and the time goes by fast.
Going to the gym between 4pm to 7pm will guarantee you to be in a large crowd. Some people find it very motivating and like the challenge of meeting friends this way.
You could also pool together with your roommates and purchase at home workouts such as P90X or Insanity. These are challenging and require no equipment. Then, you can workout any time you want in your room or living room. You can find similar workouts on YouTube, but it might not be the full version and could be missing key elements for the full benefit and safety.
You can also take advantage of campus recreational opportunities such as late night open gym and intramural sports; you can put together a team with your classmates or a group from residence. This is included in your tuition and is a great way to blow off steam and rev your competitive juices.
Don't give up, especially when the school workload heats up. If you skip a day or two, don't sweat it, but work hard as soon as possible and stick to a routine.