Frequent and open communication. You can do free video chats with Skype. I'm not a relationship expert by any means, so maybe someone else will have better ideas.
Answered Nov 02, 2011
Edited Nov 02, 2011
I gave a lot of ideas in this post:
http://www.ehelp.com/questions/10443064/how-do-you-keep-a-relationship-going-with-someone-who-lives-in-a-whole-other-to