Check out my latest tip for your serve .
See my photo below.
I must have thrown over a million Tennis balls in the air in 25 years. I have practiced and practiced.
A simple way to get a better ball placement is to put your racket in front of your front foot. Your aim is to get the ball to land on the strings. Keep your arm straight and hole the ball loosely. See how many times you can hit the racket. 
Simon 'H' Tennis 