It can be easy to let relationships fade if you don't see someone everyday, but with just a little effort you can keep in touch.

[edit] Steps

Collect cheap greeting cards. You can buy common ones in packs. Many greeting cards are available for as little as 99 cents. Whenever you are at a store that sells cards, make a point to pick up an inexpensive one.
Write down the birthdays of all the friends and family members you want to acknowledge.
Take out your birthday list at the beginning of every month. Send a card to everyone with a birthday this month (Yes, the people at the end of the month will be getting their cards very early but it is better than getting them late!)
Send a holiday card to everyone you'd like to stay in touch with. Even with minor holidays like St. Patrick's Day you can find a pack of cheap cards in the store.
Start a web page or blog. Myspace is a very popular site. Let your friends know where to find you.

[edit] Tips

Call your friends; it takes no more than a "how are you?" or "what's up". Ten minutes on the phone can mean so much to a loved one, but doesn't take more than the 10 minutes of your day.