One of the most common swing errors I see on the lesson tee has to do with your head. The problem? You move it forward as you come through the ball which means you can top the ball, send it left or right. Well, just about anything can happen and it usually does. Your head get "ahead" of the ball.
One great image to help keep your head still is to imagine a glass of water on top of your head. The trick is ... don't spill it! Check out the video and you'll see what I mean.
Enjoy the game again!