Try this:
http://www.mayoclinic.com/health/joi...ection/AR00027
Most of these tips apply to people who already have significant arthritis but the larger point is that doing things in a way that doesn't put undue strain on joints is a good idea. Some ways of doing things can concentrate a lot of force on a single joint. Finding ways to spread the force out (e.g., using the whole hand rather than just the fingers to twist something) will lessen the strain. Also, avoiding placing joints in extreme positions (over-flexed or over-extended) will save wear and tear. Unfortunately, a lot of what we do when we play guitar (fretting, fingerpicking, even twisting tuners) can load up joints with a lot of force. If you can do it without pain it may be okay but when it can be avoided, so much the better. As an example, when changing strings, a string winder will transfer force from the thumb and index finger to the hand and wrist, exerting considerably less force on any one joint.
Another specific example: I find that the "right" way of holding a flatpick, with the index finger tip curled so that it's parallel to the palm, puts a lot of lateral pressure on the middle knuckle of that finger. I've modified my grip in a way that some players might scorn but that I'm pretty sure will save a lot of joint trouble down the road.