An area of extreme importance that is often overlooked is armrests. Poor adjustment, or lack of available adjustment can contribute to upper limb disorders: shoulder and neck pain. Do spend a couple of minutes getting them correct.
The amount of adjustment available on armrests varies as much as the entire chair. If the chairs seat is particularly wide, it might not be possible to bring the top of the armrest in close enough to the body.
Adjust the width of the arm rest so that your elbows rest comfortably on them without having to reach out. Some are adjusted at the base of the arm, where it enters the chair, on others the top pads slide independantly of the arms. Your elbows should remain under your shoulders.
With your hands resting in your lap bring each armrest up so that they rest just onto your elbow. It’s important not to raise them too high.
Often there will be adjustment forward and back, usually just the top pad. When typing push the pads forward, not so far that they get in the way of the desk, but so that with your elbows rested on them, your wrists can comfortably reach and rest in front of your keyboard.
Some have turnable tops. When typing, turn the tops inwards to reduce lateral movement of the wrists.
Some armrests angle forward or back from the chair to the pad, and can be fitted either way. They should never impede access to the desk, so for slimmer people, the armrest will need to be fitted so that they angle back. Larger people may need them fitted so that they angle forward in order to benefit from them.
Now you have the chair correctly set for you, bring it to the desk. Ideally, you’ll have a height adjustable desk, and position it so that the table top is level with the armrests.
Most will not have this luxury. Shorter people will need to raise the chair, and use a foot rest. Taller people should avoid roudning the shoulders and bending their neck. Ensure screen are placed so that the top of the viewing area is at eye level. Desks raisers placed under the feet of the desk are a cheap an effective way of raising the enitre workstation.