Welby van Horn, one of the best coaches of all time said, ''Developing ball control, before adding power, should be your formost goal when learning the game." I think this applies to the serve as well as all other tennis shots. When you can put your serve where you want it consistantly then it is time to work on power.My humble opinion anyway.
"get your facts first, then you can distort them as you please." Mark Twain Prestige MP VS 50#