Do two to four sets of squats, followed by two to four sets of leg presses (pictured here and next slide), then two to four sets of quad extensions. Do 10 to 15 reps in each set

Squat
Stand with your feet slightly wider than shoulder-width apart and your toes pointed straight ahead. Drop your glutes back, as if you were sitting in a chair. Keep your chest lifted, your abs tight, your weight toward your heels and your knees behind your toes throughout the exercise. Avoid rounding your back; instead, maintain a natural, slightly inward curve. Descend until your thighs are parallel with the floor and then push upward from your heels to return to the starting position. As you improve, hold a barbell across your upper back, just below your neck. Stick your chest out slightly so that your shoulder blades come toward each other.

Leg press (pictured here and next slide)
Sit or recline in a leg press machine and adjust the seat so that your torso and thighs form a 90-degree angle in the ending position. Place your feet flat against the platform with your toes pointed either straight up or slightly outward. Keep your knees in line with your toes throughout the exercise; don’t let them sway inward or outward. Lean against the seat back, and press the platform up with your feet until your legs are extended. Slowly lower to the starting position. Variations: Push with two legs, and then lower with one. Or push down and up with one leg, and slow the pace with a count of eight up and eight down.

Quad extension
Sit in a quad extension machine. Adjust the seat so that it supports the entire back of your thigh, and adjust the leg pads so that they are just above your feet. Align your knees with your hips. Lean back against the seat, and contract your quads. Lift your feet in a slow, controlled motion until your legs have only a very slight bend at the knees. Pause, then slowly lower to the starting position.