You must stay in touch on a daily basis. You have to be available to one another despite the fact that you are not physically together. And when you do talk each day, don't just talk about love; you must keep each other informed on the day-to-day aspects of your lives. This way each of you is aware of how the other is thinking, feeling and developing. Late-night talks and thoughtful letters can convey a lot of what is most important in the long-term: your goals, values and dreams.
In long distance relationships, you must make your marriage a high priority by making sure you see each other on a regular basis. You have to have a lot of quiet and quality alone time for healthy sexual enjoyment of one another. You don't want your limited physical time together dominated by hanging out with friends and relatives. You may find that if you handle this part of your relationship right you will have a more satisfying and pleasurable marriage sexually because you cherish these times more than those couples who see each other every day.
The one thing that most people who have successful long distance relationships seem to have is flexibility with one another. You have be able to adjust quickly to different circumstances and situations. You can't get angry or jealous if one of you needs to change your daily talk time for one reason of another. You have to avoid being possessive, paranoid and insecure because these things will destroy the trust and love in your marriage. As long as you both trust each other, communicate openly and regularly keeping each other informed about what is going on in your daily personal life and maintain a normal healthy sexual relationship when you are together then you can have a successful long distance relationship and marriage.