Focus on toes pointed out leg extensions and partial squats utilizing the top half of the movement. Full squats with chains and high box squats also are good options.
“The researchers had 10 males perform the squat jump while measuring the muscle activity of the vastus medialis (teardrop) and vastus lateralis (outer quad muscle) using electromyography (EMG). They reported in the journal Medicine & Science in Sports & Exercise that during the first half of the squat, the muscle activity of the medialis was about 20 times that of the lateralis, while in the lower half of the squat the muscle activity of the medialis and lateralis was about equal.”REFERENCE
Toumi, H., at al. New insights into the function of the vastus medialis with clinical implications. Medicine & Science in Sports & Exercise 39(7):1,153-1,159, 2007.
FORMING TEARDROPS. Stoppani, Jim Joe Weider's Muscle & Fitness, Feb2008, Vol. 69 Issue 2, p258-267, 2p, 1 Color Photograph, 1 Graph
Stoppani, Jim, and Rob Fitzgerald. "Redefine chain training by Using these new techniques to stimulate: massive muscle growth. " Joe Weider's Muscle & Fitness. 71.1 (Jan 2010): 142(8).