Barbell Squats Are Great Thigh Exercises
Barbell Squats:
NEVER take your heels off the floor. this is very bad form, I've taken weight training for two years, and you should never ever take your heels off the floor.
It makes you unbalanced for one, two, you could pull a muscle (usually calf muscles) and three: ALWAYS HAVE A BUDDY! Even if you are going light, you never know when you will loose your balance and fall backwards or even forwards with the bar on your shoulders.
Thanks for reading, and I hope you take my advice.