Set up a flat bench at the back of the Smith Machine "cage" and stand in front of the bench so that you are about a foot to a foot-and-half away (depending on your height) from the bench. Of course, the loaded Smith Machine bar will be on your back and you will be ready to unhook the safety lever to begin your initial squat. You will have ONE foot on the bench (toes-first) and the other firmly on the floor. This is your starting position.
Unhook the safety and squat down all the way until your back leg's knee is a few inches away from the floor. Then, as hard as you can, push back up with your legs and get back into the starting position but don't completely lock-out your front leg. You should always keep tension in your leg for optimum results.
Finally, repeat the entire movement for the desired or prescribed number of repetitions and then rest a few seconds and switch and do the same movement with your other leg.
Perform this exercise in a smooth and fluid motion
Keep your back straight at all times
Don't lock-out your front leg at the top portion of the movement
Don't do this exercise if you are a beginner
SPECIAL NOTES & LEVEL of DIFFICULTY VARIATIONS
To increase the level of difficulty, slow down the movement or increase the weight.