Mobility. Arthritis of all forms tends to rob you of your joint motion. As a result the soft tissue envelope around the joint then also get tight. I would recommend stretching around the affected joint as well as the joint above and below. Both static and dynamic stretching are helpful as well as active assisted stretching.
Many things. Depends on the type of arthritis. For most people with osteoarthritis which is the most common form. It is important to keep the affected joints flexible and not stop moving. Some form of daily exercise is best. Your doctor should be able to advise the best exercises for you. Eat healthy whole foods, avoid too much red meat, fried foods and foods with additives. Yoga if ok with your md.