Keeping proper posture would seem like it was an easy task. The truth is that most people have a hard time sitting up straight, keeping their feet flat on the ground, and having their keyboards, monitors and mouse at a proper distance and height.
The desk:
Most people don’t put much thought into the type of desk they will buy. Desks can be more than furniture; they can be used to make repetitive office work less stressful. The ideal desk height is one that will drop just at the elbow level, not above. A worker should be able to maintain a forearm-to-upper arm angle between seventy degrees and one-hundred-thirty degrees while sitting. Workers may vary in preference in the height of their desks depending on the task being done, but this height should always favor the healthiest wrist and elbow placement.
Foot rests:
These devices are commonly used by shorter people who cannot reach the ground while at their desk space. Footrests are used to foster the sensation of the feet planted on the ground, rather than dangling precariously above it. They can help remove stress from the back and keep the worker from crossing their ankles or knees, which can lead to back, hip and knee problems.
Mouse:
These days, most mice have a raised surface with a trackball in the center. Others look more like joysticks used for computer games, and some people prefer to use a digital pen and tablet. Each of these devices was designed to lessen the usage of the wrist in an uncomfortable, unnatural way. Which device a worker will use ultimately depends on the worker’s preference.
Keyboards:
Typists, unless they already have an ergonomic keyboard or a wrist support on hand, will typically arch or bend their wrists. When a typist has a wrist support they may become dependant on it and bend their wrists, instead of moving their forearms to type. The transition from traditional to ergonomic keyboard can be awkward at first. Typists usually type slower and make more errors when first introduced to the change, but over time speed returns to normal and the need for corrections lessen.
Ergonomic tips:
Hands, wrists, and forearms are straight, in-line and roughly parallel to the floor.
Head is level or bent slightly forward, forward facing, and balanced. Generally it is in-line with the torso.
Shoulders are relaxed and upper arms hang normally at the side of the body.
Elbows stay in close to the body and are bent between 90 and 120 degrees.
Feet are fully supported by floor or footrest.
Back is fully supported with appropriate lumbar support when sitting vertical or leaning back slightly.
Thighs and hips are supported by a well-padded seat and generally parallel to the floor.
Knees are about the same height as the hips with the feet slightly forward.
Information provided by:
http://www.keyboard-ergonomics.com/