Lesson 3: Coordinating your should rotation and swing
Again, just about everything is in the video.
One thing I didn't include (it will be a focus for day 4) is keeping all parts of your arm and grip loose. A tight grip leads to flexed muscles which reduce freedom of movement. So, don't have a death grip - it should be loose and relaxed (just don't go so loose that it flies out of your hand).
I think I swing a little bit harder in this video than yesterdays, but I'm still only at about 50% to avoid injury. There is also a video on strengthening your rotator cuff in the Homework section. That is HIGHLY recommended for preventing injury and adding power to your serve. You should be using very light weights (1 pound, can of soup or bottle of water).
20 swings with shoulder rotation added (50% speed max)
Take a little break.
20 more. Little break. 20 more. Little Break. 20 more. Little break. 20 more.
Watch this video and start doing these exercises. If you have therapy or exercise bands (low resistance ones), you can also search youtube for exercises that use those.