I see way to many people with horrible squat technique at the gym. Doing them wrong will limit your gains and could cause serious injuries. Squats are by far the most effective exercises for building leg muscles.
How to do a proper squat
- Legs a little further than parallel
- Bar resting right behind your neck
- Keep you face aimed forward and do not look down
- Go down right below parallel or 90 degrees. This is actually better for your knees than stopping before parallel
- Do not take a rest in between reps. One continuous motion
Here is a good video to show you the proper form: