Ergonomics. Get a real professional to evaluate your workstation and recommend placement of monitor, keyboard, and chair.
Gently stretch out your hands, wrists, and arms before you begin an extensive keyboarding session. Pay attention to your posture too.
I started getting a lot of wrist pain in 1998 and I had to change a bunch of my habits. To this day I wear wrist braces while working at the computer (I use the IMAK SmartGlove).
Don't play too many video games, that just increases the hours you spend torturing your hands and wrists.
Also, drink plenty of water and exercise regularly. Lay off the soft drinks.