Sometimes you really need to give credit where it is due. RacquetFlex does very well on videos in general vs his Youtube competition and also hits on many of the most important aspects to improve. It's not perfect, but in this video on serving, he does a very solid job of pointing out the key arm structures on the serve that will enable pronation to supercharge your serve. I'm starting a series on the CongruentTennis "Serve Code" that will first layout the 4 phases of the serve, then go into many of the details of each phase in following articles. The Serve Code was developed during 1999-2001 using high speed video on 3 of the best Servers in history: Pete Sampras, Goran Ivanišević, and Richard Krajicek.
Enjoy this nice work by RacquetFlex that I find to be one of the top 2 serve videos out there right now.