Working at a computer all day long will strain your eyes. The best, and easiest tip to remember is 20/20/20.
Every 20 minutes, focus on something 20 feet away for 20 seconds.
Oh, and blink a lot.
This and a bunch of other good ideas are summarized in this Wired article.
The Mayo Clinic has a few recommendations as well. I particularly liked the eyelid massage.
You can even get special glasses designed to help protect your eyes when you’re working on a computer. I haven’t tried out these Gunnar Glasses, but if you have, please leave a comment with your experience!
Educated yourself and be good to your eyes!