Overhead squat–this is performed specifically for technique. These locks in the back keeps the chest up, the head up and allows you to work specifically on perfecting the technique for proper squat lifting.
Back squat—with the feet just a little wider than the hips, feet rotated out just slightly keeping the back locked in and the chest up. Emphasis is on sitting back and down, so that the knees do not rotate forward, head should stay up but not looking towards the ceiling, so that we lock the spine in place. Slowly control on the down, explosive on the up. These are great exercise for all sports.
Front squat—with the elbows out in front, keeping the barb back on the chest, this will isolate the quads and the gluteus more for better development for explosive things such as jumping and sprinting. Again we want to make sure that we lock in the back and sit the hips back so that the knees do not roll forward.
Single leg squat—here we want to isolate again the body limb to make it more dependent upon balancing right side and left side. A lot of times when we do squat one side will do more work than the other. This will isolate each leg making sure that we develop equally on both sides. Same technique as we do in a squat rack, we want to try and simulate here in terms of doing just a straight squat off in the box.
Start tall, sit the butt down and back, drop down deep, squeeze back up. Use the arms for balance in this case, throw hard and leave them straight down. We want to drop down so that our hip goes to at least our knee heights and then squeeze back up. In some cases all the way down so that the buttocks touches the heel.
For more added resistance—a moderate overload, not a heavy overload, to begin with. Simply dumbbells can help to add the resistance.