Make a commitment. You and your significant other should have an understanding before the two of you go away to school about the status of your relationship. Decide if you are going to remain an exclusive couple or if you are okay with each of you seeing other people. If the two of you have opted to stay together, verbalize that commitment to one another so that it's clear and understood by both of you.
Stay in contact. Keep the lines of communication open to keep trust intact. Even with the distance between you, there are still lots of ways to bridge the new gap and keep the relationship close. Making sure that the other person knows about all the current things that are going on in your life is the best way to avoid him feeling excluded or left out.
Be supportive of one another. You will each be facing new challenges with course loads, life away from home and away from one another, roommates and all sorts of other things. Even with the distance, it's important to be there for one another and support each other in all your new endeavors. Let your significant other know that you are there for her, that you believe in her and that you are sure she will do great. Make sure that you are as supportive of each other from far away as you were when you were living close to one another.
Remember the important dates. Just because you are in a long-distance relationship does not mean that you should forget the dates that are important to both of you, like birthdays and the anniversary of your first date or your first kiss. Plan to be together for these special times, if possible. If not, let your special someone know that you are still thinking about him by calling or sending flowers to make sure it is still a special and romantic day.
Surprise each other. Nothing keeps the spark in a relationship like a little spontaneous romance. Plan a trip to your girlfriend's campus and surprise her for a weekend. Showing up on her doorstep with a cute gift and a smile is a great way to let her know that you have been thinking about her even when the two of you were miles apart.
Be faithful. The temptation to cheat may be greater than ever both because of the increased distance between you and because of all the exciting new people you will meet at college. If you care enough about your significant other that you chose to stay together, then respect him enough to remain faithful to him. If you don't feel that you can do this, it's time to reevaluate the situation.
Trust each other. Distance can make it easy to start to doubt someone's faithfulness, but distrust will weaken the bond between you and cause tension that will lead to fighting and accusations. If you are being faithful, trust that your partner is, too.