If squats are the mainstay of you leg training routine, and you want to increase the recruitment of the vastus medialis muscles, you have the choice of a) using a specific foot position b) overloading the bottom position.
The foot position that will maximize the recruitment of the vastus medialis will call upon placing the load on the arch of the foot.
This is best accomplished by using a narrow stance and elevating and moving forward the center of gravity of the body by using something to elevate the heels.
By doing more work in the bottom position, you will increase the recruitment of the vastus medialis muscle, since this muscle is responsible along with the hamstrings from getting you out of the bottom position. Knee injuries are fairly common in team sports, I suspect strongly that one of the major cause is the improper ratio of strength between all heads of the quadriceps and the hamstrings. This off-set ratio comes from all the poor range squats (coming from strength coaches obsessed with claiming big numbers for their squads) and many partial movements such as the hang power cleans.
When interested in developing the vastus medialis muscle, there are two techniques used by the Olympic athletes I coach that you may want to use:
Cyclist squats: Olympic level cyclists used that exercise to attain World Record performances in the track events. In this variation of the back squats, you want to use a board to rest your heels on in a narrow stance (4 to 6 inches between the heels). The best type of board for this is wedged, so to that the pressure on your feet arches is minimal. The higher the wedge, the more recruitment of the vastus medialis you will get. You will also find that you will squat more upright when using the wedged board, so less recruitment will occur in the gluteal muscles. As far as reps and sets are concerned, the German Volume method applies particularly well to this exercise if you are truly motivated at hypertrophying this muscle.
One and a quarter squats: This one is used in training Olympic skiers to off-set their enormous development of the vastus lateralis muscles and prepare their knees for the risky situations they get into. Squat down for a 5 seconds count until you hit bottom position, come up a quarter of the way at a slow and deliberate pace, go back down and come upuntil your knees are short of lock-out. That consists of one rep. Performing 4 -5 sets of 4-8 of the one and quarter reps will set your vastus medialis muscles to record growth
Give a fair try to each one of these variations for six different leg workouts. I am sure you will pleased with the results.