Here is a simple tip I discovered myself: don't move your body forwards or backwards during the ball toss. Of course the striking hand will start moving. But don't move the upper body till the ball has left the hand, thinking it will give you momentum or something. James Blake is a good example of a guy who keeps a steady upper body during the serve. The ball toss is much more consistent if the body is still. Second one I discovered by observing a teaching pro recently. His left foot is not at 45 degrees to the baseline or even pointing to the net post - it is almost parallel to the baseline. As he uncoils to strike the ball, the foot rotates till it is about 45 degrees to the baseline. I found that this gives freedom of movement to the foot allowing it to adjust to the upper body motion instead of being stuck there. Of course this is for those who bring the right foot forward, not for those who lift off the ground.