[cpleppert]

Surprised that he didn't mention:

1. stretches

Do this before any extended typing session: http://www.youtube.com/watch?v=SSbf4mBKq-o Doesn't have to take more than 30 seconds, just DO IT

2. height of the keyboard

The vast majority of desks simply aren't the right height. Your hands should be comfortably pointed down and not over your wrist. Had some issues with wrist pain a couple years ago, never had any problems since.

[rowanseymour]

I definitely second both of these. The nature of my work means I end up using my computer in all sorts of places. Even just one day of trying to type on a desk that's too low, too high or too far away (i.e. there isn't room to get your legs under the desk) and I get problems. My back has to be vertical, and arms have to be horizontal.