Squats in general are one of the best overall exercises because it involves almost every muscle in the body. The best advice I can give you when it comes to squats is always have your knees and toes going in the same direction. When you squat down, keep your knees behind the toes the best you can. AND to keep your weight in your heels. Your toes should be able to wiggle around in your shoes.
Squats on a Smith Machine with plates ( I like to use the 10lb plates for their thickness ) under the heels helps with learning the feel of keeping your weight in your heels. This is a good beginner squat exercise. I don't like to go heavy with these (I have on a 25 lb plate on each side in the video) since I am trying to go as low to the ground as possible. My feet are out in front of me barely to where my body is on a slight angle. My feet are just a little bit wider than shoulder width apart and toes SLIGHTLY turned out (NOT a sumo/plie). Squat down keeping all your weight in your heels and your knees and toes going in the same direction during the entire movement.
The active rest is just like Lunge Jumps but try them from time to time on a bench or a box. I like this one because it allows for you to do a deep lunge.