Learn how to perform a variety of Squats that will help strengthen your Quads. It is important to learn the form so that you can work the muscle you want to, but also prevent injury.
Quadriceps (quads) are the largest muscles in the leg. The best way to grow heaps of muscle is to do lots of squats with many variations (do only one or two types of squats per training session). Squats are good because they hit all four heads of the quadriceps; adductor brevis, vastus intermedius, rectus femoris, and vastus lateralis. There are many other very good exercises that work the quads.