While most solutions are very personal and unique, there are some broad guidelines that one can follow in attempting to create a comfortable environment. Your table should be high enough off the ground so that you can sit and work with your hands comfortably level, preferably parallel with the ground. There should be at least six inches of desk space between the edge of your desk and the keyboard and mouse to provide support for your wrists while you work. Your monitor should be positioned so that you can look at it without raising or lowering your head more than fifteen degrees from an imaginary line parallel with the ground. If you have a computer in a tower case, chances are you will need to buy or build something to raise it at least four inches off your desk.
Chairs are a special case.
The most commonly bought piece of furniture is often the one given the least consideration. I have two compressed lower vertebrae and it is ridiculously easy for me to sit myself into days of pain. After one particularly ill advised two-hour session that left me bent over double and squinting with agony for another three hours, I vowed to replace every regularly used chair in my home office with one that provided proper support. My regular chair is a large executive model that has been tweaked with a lumbar roll, a lump of foam that I directed the upholsterer to place in the lower part of the chair back which changes the way it supports my spine. I mention this because in my travels to various office equipment stores in search of new chairs, I found that generally, large, expensive executive chairs provided the worst back support.