Help on kicking and keeping my heels down?

One of the biggest mistakes people make is forcing their heels down. You are probably concentrating more on that than the actual motion of squeezing your horse. Your feet should be in the position like you would have them if you were standing flat on the ground. Keep the ball of your foot on the iron and keep your heel level, And as it was said in an answer above, squeeze rather than kick.... Also make sure your seat is correct. Your proper control of the horse comes from your position in the saddle. I found that when I was learning I was too busy flapping about everything else that my seat position was wayyyy off!! I had a private lunge lesson and my seat corrected almost instantly. I then found it easier to keep my heels down and kick on. Remember, keep your ankles loose too, you need to feel comfortable, or your horse wont feel it too!!