I'm currently in a LD relationship with my Master and the biggest part is that you have to be honest with each other. I guess this has already been said in this thread, but I can't stress it enough. Modern technology helps out a lot, texting, IM services, Skype, and the like are all good ways to communicate throughout the day. The only warning I have for you is that nothing anyone could have told me would have prepared me for how hard it is to wait to be able to relocate myself to be with Him.

In a lot of ways I think relationships starting out LD and moving to RL can help make a relationship much stronger if you can make it work long enough to be with each other physically. The communication skills you develop in a LD relationship are invaluable over the course of your relationship.