Here is an adaptation of an exercise from my book Physical Expression on Stage and Screen. You don't have to be a performer to benefit:

1. Sit at the computer as you do normally.
2. Notice how you are using your body.
3. Do you hunch down toward the computer?
4. What's happening in your head, neck, and shoulders?
5. Do you hold your breath, or make your breath shallow?
6. Remind yourself to lengthen easily into your full height.
7. This does not mean military posture.
8. Allow your neck to be free, your torso long and wide, and breathe easily, as you type.

Here is a video exercise to help you when sitting at the computer. It's less than 2 minutes long:

http://bit.ly/1DznoIn