Your thighs should rest comfortably level with a 90 degree angle to both lower back and knees. The back rest needs to be adjustable as well. Maintain arms vertical at your sides with elbows at 90 degrees. When typing hold wrists and hands straight or just slightly downward, using a wrist rest when at rest. Eye breaks are important at ten minute intervals, look around and focus on something in the distance.
Body breaks are also important.
Every twenty to thirty minutes, stand up and stretch, or perform other duties that give you an opportunity to walk away from the monitor. Use subdued overhead or desk lighting and keep an ambient temperature comfortable to you. If the thermostats are locked, bring in a fan or heater. One size does not fit all and what works for you may not work for the next person. Try different combinations until you hit on the right one.