Ergonomics helps keep your body healthy and reduces the risk of repetitive strain injury, and complications due to restrictions of circulation and skeletal pressure. An ergonomic chair designed for working long periods of time, and a height adjustable desk, are the foundational blocks for an ergonomic setup at work.
Seat height: adjust your chair such that your knees form a 90 degree angle, and your thighs are roughly parallel to the ground. If your chair doesn't go low enough, a foot rest can help bridge the gap.
Seat depth: adjust your seat forwards or backwards and allow for 2"-3" from behind the knee to the front edge of the seat. Make sure you're sitting all the way into the back of the chair, with your back engaging with the backrest of the chair.
Arm height: adjust the arms of the chair such that it is level with the height of the desk.
Arm depth: adjust the arms of the chair forwards or back so that there's no gap in-between your arms and the desk.
Arm width: adjust the arms of the chair side to side as close to your body as possible.
Arm angle: adjust the angle of the arms of the chair so that there's no gap in-between your arms and the desk.
Seated Desk Height: adjust the height of the desk when sitting in the chair so that your arms fall comfortably on the desk top. Your shoulders should not be shrugged up, or sloping downwards - you should be able to rest your arms comfortably and naturally on the desk top.
Standing Desk Height: adjust the height of the desk when standing so that your arms fall comfortably on the desk top. Your shoulders should not be shrugged up, or sloping downwards - you should be able to rest your arms comfortably and naturally on the desk top. Your feet should be shoulder width apart.
Monitor height: Adjust your monitor height such that the top of the monitor is eye level, or even slightly lower. If your monitor is not height adjustable, then use a book or a box to elevate it.
Monitor angle: Position your monitor such that your content is visible straight-on, and you're not turning your head to see your primary content.
Monitor tilt: Adjust the tilt of your monitor such that the bottom of the content is comfortable to look at.
Laptop height: Set your laptop such that the top of the display is eye level. Use a laptop stand, a book, or a box to elevate it.
Monitor / laptop display distance: Set your monitor or laptop display distance to be about 20" in front of you. Roughly, an arms length when sitting is a good rule of thumb.
Feet: Your feet should be in front of you and flat on the floor
Back: When sitting, make use of the ergonomics of your chair and rest your back on the backrest of your chair. When standing, your back should maintain the natural curve of your back.
Postures: Changing your posture frequently is good for you. Reclining, sitting upright, standing... all are great postures to keep you working comfortably and prevent injury.
Chair recline tension: Adjust the chair tension such that the chair holds your body up without pushing you forward.