There are three key things that you need to have in a long distance relationship if you want it to last: trust, commitment, and scheduling time for each other despite the miles in between.
Trusting your boyfriend/girlfriend is huge in any relationship, but more so in a long distance relationship because you don't get to see them on a regular basis. I won't lie, it can become a challenge to trust them at times, but if the relationship is meant to work out, it will. Unless they've given you reason to mistrust them, you put your whole heart into believing them. This leads into commitment. In a long distance relationship, you both need to be committed to each other.
Whatever that commitment is, that's decided between the two of you. Once decided, you stick to the agreement. May that agreement be waiting till you can be together, or being with other people while apart, its up to you. For myself, we are fully committed to each other and make sure the other knows that. Lastly, making time for each other is something couples dealing with distance often times forget to do or don't see how it is possible without seeing the other in person.
So here is the deal, it is crucial and important to make time for each other. With technology what it is today, we really have no excuse to not make time. In my own relationship, we text each other every morning and every night. As well as calling each other on a daily basis no matter how late. Skype has also been a huge help for long distance relationships. Not only do I get to talk to him, but I can see him as well. It is the closest date you can have without them physically being there.
Another thing I've found lately that gives us a sense of connection still, is scheduling date nights. We have had a total of three so far. Date nights work by planning an activity you can do in both paces such as seeing a movie or going to an amusement park. Once the activity is picked you pick a time you are both able to do and do the said activity at the same time. Then you can come back and share your experiences together. But if this doesn't help, sometimes the best thing to do is take a break.
I've learned this to be the best thing for our relationship when we feel like we can't stand the other at the moment. Taking beaks sometimes let you take a breather and evaluate your relationship. It lets you see if you're happiest with this person, or without. For the most part, it makes you see just how important your boyfriend/girlfriend is to you by not having that contact anymore. Hopefully this answers your question and gave you ideas of how to improve your relationship all around. Every relationship is different, but these have been the things I've found the most useful in my own relationship.