One of the things we work on with overheads is to not point at the ball. The overhead requires a good shoulder rotation and pointing at the ball doesnt help you achieve that. If you need to point, a better option is to point at the ball with your non-dominant arm elbow.
The key with the overhead once you establish where your going to hit it, is to not start focusing on other things like where your opponent is. This causes your eyes to drop and most likely your head will follow.
The number one reason players have trouble with overheads is a dropping head just as or slightly before impact. Keep the head up and watch the blur of your arm go by.
You should also hit an overhead with a serving grip. You have to perform slight adjustments with a eastern forehand grip to sqaure the racquet to the ball. These adjustments (with a ball dropping very fast) can cause a number of errors and inconsistencies. I would suggest you practice with a Continental grip for your overheads. Remeber you dont want a lot of stuff going on with the overhead. There is enough "calculating" going on to meet the ball properly.