How do you reduce your chances of getting arthritis and strengthen joints?

Nothing Yet. There is nothing we know of that will prevent the onset of arthritis. There is a lot of research being done but nothing that has great promise as of yet.
Preventing Arthritis. We know that joint trauma, aging, obesity are factors that promote the osteoarthritic form of arthritis, sometimes as early as the thirties. Protecting your joints by choosing healthier exercises patterns when younger, continuing to exercise with your joints mildly (proven to help), keeping your weight down to normal, all help.