Having been in a few failed long distance relationships and one good long distance relationship (Yeah! Still alive!) I have no illusions about the challenging aspect of managing a serious relationship with someone you care about.
Plan to visit each other when you can. When you visit, make everyday count-do something memorable-even if you don't leave the house-you could have a game night, play video games, etc.
If you live across the country from each other- plan to meet somewhere in the middle and have a fun adventure together.
When I started dating my SO, he was working long hours underground without any semblance of interaction besides his email for most of his days. Since my job involved traveling to his city at least once a week-I would leave him notes on his vehicle. They weren't always sentimental and full of hearts, hugs and kisses-but it was enough to show him that I was thinking of him.
Video chats-whether it is Skype, Yahoo, MSN Live, Kinect or whatever other video service-it is worth it. You get to hang out with them online, and if you both of kinect-you can get the same games and play with them while you talk.
As a side note-Skype was a lifesaver for us while we were deployed. (that's right, we were both deployed at the same time. It can mean everything to be able to just see your sweetie sometimes.)
Send small gifts to each other. This doesn't have to happen very often, but sometimes when you want to show you care or that you have been listening-it can been received as sweet, caring and thoughtful.
Try something new together-hiking, skating, horseback riding, skydiving....when you are together.