The best way to prevent sprains or strains is to keep yourself in good physical shape so that your muscles, ligaments, and tendons are strong and flexible enough to resist trauma. To prevent recurring injury, ask your doctor or physical therapist for exercises designed to rehabilitate the muscles in the injured area.
You may benefit from a brace to protect the area while you are recovering from a recent injury. Use a brace for only a short period, because your muscles can get used to the support from the brace and eventually weaken over time. If you're overweight, ask about an appropriate diet and exercise program to get closer to your ideal weight.