When performing squats my heels lift and my balance is not very good. How can I improve my squat technique?

It sounds to me though you may have tight hamstrings and calf muscles, this would account for the heels lifting. With regards to your balance this could be due to a number of things, one of them being a weak inner unit (core muscles).

I would suggest you see your gym instructor and ask for a calf/hamstring flexibility program and core conditioning program.

If you have no luck in obtaining these programs give me a call and I will try and fit you in my diary somewhere to show you these programs.

Good luck, Karl