Narrow squats are great for working your quads (thighs). They also nicely boost your metabolism as they work the biggest muscles in your body.
Tips:
1) Keep your feet hip width apart, toes pointing straight forward.
2) Imagine sitting back on a chair. Your weight should be on your heels and your toes shouldn't go past your toes when going down.
3) Aim to get your bum so low that your thighs are parallel to the floor. This might take time to master.
3) Keep your chest up high all the time.
4) Use your hands to balance yourself through the movement.