By the way...lunges are a great way to work the legs and booty. Take them on the move and you elevate your heart rate as well!!
Let's start with a basic, static lunge (in place)
Feet hip width apart then take a large step forward (or back) maintaining the hip width positioning of feet (helps you keep balanced.
Bend the front knee until the thigh is parallel to the ground. Watch and make sure the knee doesn't move inward or outward. Make sure that the front knee does not travel past the tip of the toes to avoid strain on the knee joint (causing more harm than good). Keep the rear knee bent and the weight up on the ball of the foot (this is the back foot). Your feet should still be hip width apart to help keep you balanced. Keep your shoulders back and your torso upright. Look ahead, not at the ground. Return to starting position.
The mistakes I usually see on lunges are not keeping your toes aligned straight. People tend to point toes out either direction, especially when they are doing lunges with movement. This puts a great deal of strain on the knees, so keep the toes pointed forward at all times!!
Take your lunges on the move with dynamic lunges (step out and front, drop knee down, return back to starting position). Diagonal lunges, backward lunges, backward lunge with jump, jumping lunges (really get the hear rate up!) and bottom 1/2 lunges shown below (like a full lunge only you really work deep into the muscle by only coming 1/2 way up!)