1. Trust each other
You're probably reading this, and thinking to yourself, duh. That's an obvious one for any relationship.
But for a long distance relationship to work, trust has to be a huge priority. Jealousy is going to play a role in any relationship. You need to both know, with certainty, that neither of you is going to do anything you wouldn't want your significant other to know about.
When you talk to each other, you will tell each other about people in your lives. And you need to know that just because one of you is spending time with someone that you could be attracted to that it is platonic and will not undermine your relationship.
I wish I had some good tips for building trust. It is difficult to do when you are not near each other. That's why it's a really hard one for long distance. You have to speak with both actions and words, and speak with sincerity.