How to stop topping my irons

I find that most Amatuers have the ball back to far in there stance. 

I would work on the first two keys, steady head and weight forward. Check out some of the threads on the forum about these subjects, specifically the swing thoughts thread, some great information there. 

If your wondering about your alignment. Take two clubs, lay them down forming a cross, then use that as a reference for ball placement. Depending if you keep your stance the same width for every iron shot, or shorten the stance will dictate were the ball will be. Keeping the stance the same, you must vary your ball position in your stance. Shortening the stance, you can keep the ball position near the same area.

Well, trying to help the ball in the air, could just be a side effect of straightening the forward leg to fast, and loosing the angle in the hips. So i would really look at striking down on the ball as something you need to be concerned about, if you take care of the other problems, then its hard not to hit the ball first

Ball placement notwithstanding, when I start topping/hitting thin it seems generally to be connected to not shifting my weight properly so that most of it is on my left leg when striking the ball.  This is one of my personal bugaboos and, of course, may not be your problem at all.  But it is something to check yourself on. 

In my case, I don't think it is directly connected to trying to 'lift' or 'scoop' the ball so much as simply poor swing technique, but I believe a person would do basically the same thing when trying to 'lift' a shot.  In any case, getting my weight shift right seems to facilitate hitting down on the ball at contact and much better results in general.

another thing to pay attention to is looking up early trying to see where the shot is going.  If you do this then you will naturally pull your body up and thus, your club which will give you a thin/topped shot. 

Your head shouldn't stay perfectly still but you should definitely stay focused on the impact zone until the clubhead has come through it.

Are you topping it on an upswing or a downswing?

If upswing then your swing is bad and no one thing is going to help you until you get your swing fixed.

If downswing then move the ball slightly up in your stance.

I top the ball sometimes but it is never on an upswing. Sometimes I drift to far forward too fast trying to hit the ball low and catch the top of the ball. You've got to focus on driving the ball forward and DOWN not up. The physics of the club will make the ball go up so you don't need to help it.