I have been around the game for 60 years. I look and I listen.
The following are a few simple tips that can truly help any level of play. My tips are simple and can be applied with or without a coach.
Whatever success I have had is a direct result of seeing and then saying a few simple words. Demonstrations are also very important because so many people react to vision learning a lot quicker.
Tip 1: Early Preparation
You cannot prepare soon enough- turn your hips and shoulders before the oncoming ball bounces on your side. GET THAT RACQUET BACK!
Tip 2: Exaggerate Your Follow Through
The majority of all people, no matter what sport they play, can improve by following through when you get a little nervous or your opponent is in control of play and moving you around.
Exaggerate your follow through; do not think just hit the ball. MOVE YOUR FEET!
Tip 3: Two Bounces and You're Out
Whenever you rally, wherever you play, make up your mind that you will never let the ball bounce twice. Always run for the ball even if you think you have no chance to reach it.
Richard Williams told Venus and Serena when they were six and seven years old, "Don't think, just run and hit the ball."
Try playing on a court with no lines, whatever comes to you, it is in play.
Tip 4: Hit-Recover
So many players will hit a ball and watch the ball and compliment themselves on the shot. From now on you must hit and recover.
I suggest you watch the pros- it actually looks like the pros are recovering in the middle of their hit. I don't suggest going to that extreme. Just hit, finish and get back to position.