Good posture

I've mentioned before about good posture. You may as well search the internet, there are many sites that gives this kind of information, including pictures.

The highlighted items are:

1. Your back should be straight, you shouldn't need to lean forward to reach your keyboard/mouse/to read.
2. Your neck should also be straight - adjust the position of your monitor if necessary.
3. Your shoulder should be relaxed, hence your elbow should be on the desk.
4. Your feet should be supported - adjust the height of your chair if necessary.
5. You should be careful that your wrists aren't bent.
6. It's better to have your keyboard and mouse next to each other.
7. etc
   

The point about elbow made me noticed one thing:
In Indonesia almost all computer desks have keyboard tray - and most mice are on the desks. However, I couldn't remember seeing a single desk with keyboard tray in The Netherlands. Mostly I saw people put their computer on the corner of their L-shape desks -- but I've NEVER saw them using keyboard tray. Have you seen one?