What is the best way to treat arthritis without medication?

Depends. If you are overweight, the best means of reducing stress on your joints is weight loss. For painful arthrits of the knee for every pound you are overweight you induce anywhere from 4-7 pounds of added force thru your knee depending on activity such as stair climbing. Put down the cheeseburger and choose something healthy. You can't change genetics which probably is the most important factor.
Exercise. Swim, water aerobics or walking in chest deep water. We are about 80% lighter standing in chest deep water due to buoyancy. This will make exercising easier. Start with an amount that is relatively easy and comfortable, then repeat 4 or more days per week and add a few minutes to the program once a week, initially only add 2-3 mins per week, so you don't over do it. Don't give up and keep moving.