Yes, the glucosamine, chondroitin stuff is wonderful for arthritis. MSM is a sulfur compound which seems even more effective on stiff aching muscles, and connective tissue. It also can work wonders on dry skin and seems to improve hair coats.
It doesn't work overnight, but you often will see improvement within a month or so. A lot depends on how serious the actual joint damage is.
Gentle massage works as well on animals as on humans. Also, I've used pressure point therapy on dogs with what seemed like significant success... they will flinch or even yelp if you hit a "trigger point". You hold pressure- as firm as they will tolerate (which varies with the animal. This DOES hurt, don't think it doesn't! But it works miracles on people) for 8 full seconds. Then release the pressure, gently rub the larger area including the "sore spot", and if possible, pull gently on the leg or whatever body part will gently stretch the muscle involved. (this might mean pulling their head gently to the side, or whatever).
If your dog sleeps on the floor, a softer bed will be a kindness. If they don't like beds- some don't- if you can find a sheepskin rug, or even a tanned sheepskin, they will usually accept that. It's a wonderful cushion for old joints.
If you live in a cold climate, and your floors are chilly, consider getting an *animal* heating pad for them. I say one made for animals (although they can be a lot more expensive) because they are safer... thermostatically controlled, and pretty much chew proof. Also water proof, in case of an "accident".
You can use a rice bag for animals as well as people- just make sure it's not too hot when you give it to them. Many of them learn to snuggle up to it.
If a dog is having a bad day- like when the weather changes- give them a baby aspirin. I keep this down to the absolute minimum, but it does help. And if one is hurting bad enough that they don't want to move, it can get them exercising again- which helps in the long run.
Encourage them to exercise by walking with them, and playing gentle games. Go easy until they "warm up" a bit, and try to give them a few minutes of "cool down" as well after a strenuous play session.
Basically, treat them like you would a human with the same problems. It works.
Summerthyme