Right way to squat

The wrong way to squat:
You should not squat with your "knees". This meaning that as you descend your knees bend causing them to come over the feet excessively.
Second, having the bar too high on their backs. When the bar is that high up, you can't completely focus on squatting, your attention is divided between squatting and making sure that the bar does roll over your head.
Third, excessive bending of the lower back. This is automatically caused by having the bar too high on your back in the first place.
Do not lock your knees. This again is putting undo pressure on your knees and like I said you won't last long.
THE RIGHT WAY TO SQUAT:
First off, everyone knows that you cannot squat without a belt. Squats is one of those exercises that I can't see no one doing without a belt because of the protection it provides.

Second, you should be squatting like you’re sitting down in a chair. This way, your knees are kept from coming over your feet and you'll be squatting the right way...with your quadriceps. Plus you'll be getting assistance from your hamstrings

Now, this necessarily doesn't mean that you have to squat deep, but you can when you "sit back into it". Second, the bar placement should be across your shoulders and traps. This is where the bar can stay still and secure. Also when you do this, don't have your hand looped around the bar like you normally do on the bench press.
Using the false-grip on the squat helps to secure the bar much better and its also less pressure on the wrist. With that hand position, the bar can sit on your shoulders and traps easily. That way your focus is only on one thing....squatting.
To maximize this, have your chest out and during the squat keep your head up. If you look forward, without control, you tend to go forward.
Lastly, when you squat, do not lock out the knees, keep a bend in them during a set. This way, the weight stays on the quads and not on the knees.