As many visits as possible
Since you're working, you probably don't have much to do on weekends. During the week, live frugally and save up your money. Do all your chores so you dont have any on the weekend. Then, every chance you get, hop on the plane or the train or the bus and get to your girl!
Seeing each other once a week is quite doable. The transport gets old really quickly, though, so cultivate an interest in something you can do on the bus/plane/train. Good things include handicrafts like macrame (hemp braiding) and leathercraft; also, frequent your library and bring fine literature to read so you can sound smart at parties!
Days when you have no work to do and are lonely, get out and do stuff! Never, ever sit at home and mope. The very best thing is to get exercise; go for a walk or a jog, go swimming, or just pick up a workout book and do your routine at home.
Play loud music so the house doesn't seem empty.
Depending on how long you will be apart, you might consider a pet. Pets are excellent for making the house seem lively and providing affection and companionship (although they aren't good conversationalists). If you will be apart for only a year or so, get a short-lived pet like a fish, mouse, or hamster (warning: hamsters are nocturnal and very stupid). If the seperation will last for 2 to 5 years (until she gets her master's degree, or whatever she's studying for) get a better pet like a guinea pig (who is stupid but fun to hold) or a bird. Birds are especially good for lonely people because they will talk to you. Be aware, though, that birds can take a lot of time and patience to tame. DON'T buy a cat or dog unless you are ready for a serious companion who will need significant love and attention and a lot of active care! (if you do decide to get a pet, I'd love to help you get started--there's not much I don't know about pets after a lifetime of living in a menagerie)