I love to target shoot. Naturally, when I go shooting, I thought that having larger targets would be better for me. However, it is just the opposite. You will become a better shot immediately, even if you miss the smaller target more often. When you hit a larger target you get a false sense of improvement.
Now, apply this to your serve. "Think Small!" When practicing your serve, place 3-4 ball pyramids in the service box, one near the left corner, one near the right corner and the last one between the left and right pyramids. Now, when you play a match, you can more easily move your serve around with more confidence.
This is an example of "Thinking Small."
Good luck on the courts!