The monitor should have a distance from head between 45 and 70 cm. It's import be adjusted below the eyes, but just a little.
The keyboard should be in a position that permit working without folding wrists.
The light is important stay at the right side of the monitor.
Is important that desk allows you stay in a good position. The neck should be right when you work at computer.
The bright and contrast of the computer screen should be adjusted.