Often times players get the idea that they need to lift the golf ball. Lift comes from hitting down on the ball, any upward motion at impact is sure to cause a thin or middle of the ball strikes. I describe this motion as a swing hick-up or a sudden upward motion at impact. Getting more confident and comfortable with the club interacting with the ground will allow much better contact. Move the ball position around in your stance and see if you can find a spot when the club interacts with the ground more productively.