Hi! One of the best exercises to strengthen the muscles around the knee is the leg extention. I find this to be done most comfortably on a leg extension machine however, if you do not have access to one you can sit at the edge of a bench or table (your feet must not touch the floor)with an ankle weight on and extend your leg forward, contracting your quadricep, and then return your leg almost back to your starting position. Do this for three sets of 16 reps or less, depending on how heavy your ankle weight is.