The quality and comfort of your office chair affects your health and productivity. With so many options, picking the right one for you isn't easy. This graphic from Office Chairs Unlimited offers some guidance.
Most of the pointers are ones we've noted before in our guide to ergonomically optimising your workspace: for instance, Arm rests should keep your elbows bent 90 degrees, seat height and back rest height should be adjustable. The graphic lays it all out visually so you can see what you need to look for in an office chair at a glance (or even print this out and take with you when chair shopping).
In addition, I found this guideline on proper seat depth helpful:
A good guideline is while seated to have three- or four-fingers width distance between the back of your knees and the front edge of the seat.
So be like Goldilocks and find the "just right" office chair for you (or take a look at the five most popular office chairs):
Infographic: Looking for a New Office Chair [Office Chairs Unlimited]