(Due to the varying situations of those apart, all of these may not be available all of the time.)
Call, Skype or FaceTime as often as possible (even with a time difference). Have something to say. Be excited to see each other. Talk about anything and everything, just as you do when you’re together. Try not to focus on the negatives, but rather stay positive and upbeat.
Text or email regularly. Keep a list of questions and answers going between the two of you and use this time apart as a time to really get to know each other’s hearts. Also, know each other’s schedule and what is going on, so you can send encouraging texts throughout the day.
Write handwritten love notes, smother them in kisses and cologne, and send them via snail mail (super romantic).