"Take care of your body; it's the only thing you have to live in."
It is crazy to think about your body that way -- a house you have to live in -- forever. It really puts your lifestyle in regard to fitness and nutrition into a whole new perspective. It is essential to understand that anything you either eat, drink, or do to your body affects it in some way.
It isn't easy to say no to a fat slice of pizza. Trust me, I've been there. If you live by yourself, I highly suggest you prepare your meals ahead of time. Cook chicken, broccoli, rice, whatever you may like and just put it in Tupperware, and then you have food for the whole week ready. If you are on a meal plan, go with healthier options; have salad, or make a wrap with vegetables and chicken.
Work out and work toward goals with your physique and strength. You want to do pull-ups? Start with negative pull ups and work your way up to doing actual pull-ups. It is so satisfying to set a goal and achieve it. There are so many resources to research in regard to workouts.
Drinking -- it is college, so you probably will get drunk at some point. Now, drinking alcohol is bad for your body... Consider drinking vodka water instead of beer, and if you say no to drinking, then that's fine, too. Because what you put into your body is solely your decision, and it will show.
Your body is a reflection of the decisions you made. Think of your body as a piece of artwork you work on every single day and it will change the way you live. Be proud of your body because you deserve it!