Stand up straight and place your feet at less than shoulder-width apart. This is your starting position.
Lunge forward with one leg and go down all the way until your leading leg is bent at least 90 degrees. At the same time your other leg's knee will be just a couple of inches away from the floor. Keep your back straight and vertical and head up as if you're looking into the horizon. Then, push yourself off with the leading leg and get back into the starting position. Once back, lunge with your other leg first and repeat entire movement sequence for the desired or prescribed number of repetitions.
Perform this exercise in a smooth and fluid motion
Keep your back completely vertical; don't lean forward too much
Don't rush this movement; if you're a beginner it may take you a bit before you master the balance aspect of this exercise
SPECIAL NOTES & LEVEL of DIFFICULTY VARIATIONS
To increase the level of difficulty, slow down the movement or hold a pair of dumbbells in your hands.