Squat is one of the best exercise for building muscle and losing weight. It also shapes your butt and burns the most calories per rep. To prevent injuries keep your knees in proper alignment as you squat. There are three things my personal trainer taught me about squats:
1. Make sure that both feet remain grounded on the floor when doing a squat
2. Knees should not extend the toes.
3. Squat slowly
When you have one of those days when you feel a big weight on your shoulders DO SQUATS.