Tennis

Lean forward on front leg, toss ball (91 degree direction, not too low, not too high).
Tossing arm is straight in the air, knee bends.
Keep upper arm away from body. Turn forearm up and down continuously (slow down and some point) while keeping stable angle between forearm and upper arm until racket head point totally downward.
Unwind upward with elbow in the lead but still keep it away from body. Move elbow upward rather than forward.
Left shoulder moving down while right shoulder moving up. Upper body tilted toward horizontally. Racket on edge from behind. Right arm has big distance from head (stable shoulder and arm while moving up).
Acceleration: swing light and fast.
Snap up + press down.
Optional: both arms are straight (for preparation and reaching full length at and after contact).

Backhand:

Forehand:

Volley:

Sliced:

Pro practice:

Single Strategy:

Down the line forehand, run around forehand: wait to have an open down the line court.
Wide serve, early groundstroke: serve out wide (sliced serve), move up to take the ball early to the open court.
Moving forehand, open court volley: run around forehand on short ball to opponent's backhand, follow the ball up the net and hit a volley to the open court.
Return approach, open court volley: return down the line, open court volley. Need to return low (sliced return works well).
Run around forehand return on the ad side: hit a winner down the line (ball travels a shorter distance than cross court return).
Drop and go: hit a drop shot, and prepare when the ball is back (e.g. followed by a volley).

Double strategy:

Moving at net: follow wide serves: the net player shifts in the direction of the ball to cover the down the line return.
Shift as a team: the serve person move up and hit a deep wide cross court, continue to move up to the center line of the service box to force the opponent to hit right back to his team.

Tips:

Forehand, backhand: bend knees, distribute weight almost evenly on two legs (perhaps just a little bit more on back leg); pushes back leg straight up and off the ground (a little bit) when finish; keep upper body straight; for the backhand, do not involve too much the wrist.
Serve: distribute weight a lot more on back leg (can be helped by straightening left hand while dropping the ball down close to the body, and tossing the ball up); front leg mainly used for balancing, hip turning and pushing.

Next skill: Deal with high bouncing ball: swing volley, hit on the rise, lob, overhead, chip and charge.

String length for PS85: 6.5 of full stretching arms.