Computer Ergonomics. The above image shows how one should work on a computer. Bad sitting position encourages bad body posture which also leads to back pains, etc.
For a clearer illustration:
Head – Head back. Chin tucked. Ears, shoulders and hips aligned.
Neck – Use headphones. Do not cradle phone between head and shoulders.
Elbows – At sides – slightly more than 90 degrees bend
Chair – Fully adjustable with lumbar support in small of the back
Eyes – Level with top 1/3 of screen
Document Holder – Adjacent to and at same height as monitor
Keyboard – Same height as elbows with wrists slightly bent. Keystroke gently
Mouse – Adjacent to and at same height as keyboard
Chair Height – Hips slightly more than 90 degrees. Feet flat on the floor
It is also important if you buy a computer cart that is leveled to your body to completely follow all the instructions above.