The following is an excerpt from an article written by Nick Saviano for Tennisplayer.net:

Developing fundamentals is a very broad topic. There are so many different factors. But let me hit on what I consider to be some of the most important.

Hitting Zone

The hitting zone is defined by the distance from the side of your body to contact. It's how you position your body and arm at the hit. To develop consistent strokes, you need to establish your optimum hitting zone and consistently hit the ball in that zone. The actual contact point (how far out in front of the body you contact the ball) will vary depending on the type of shot being hit. However, your hitting zone should vary as little as possible. Basically, it should be a comfortable distance from your body that allows you to freely and effectively execute the shot.

Posture

Other important fundamentals are posture and balance. Great strikers of the ball look beautiful and graceful. It's like watching ballet. They have wonderful core strength, so when they move, the upper body is very quiet. The lower body is doing most of the work. You don't see a lot of bobbing up and down with the head. This facilitates smooth, clean movement to the ball, and good ball tracking. With good upper body posture the player's weight-the center of gravity-is between the feet as much as possible.

Head Position

One component in developing a consistent and effective hitting zone is creating a stable head position that remains still on and slightly past contact. It adds stability to the stroke, eliminates a lot of superfluous movements, and it helps to keep the player's focus on the hit psychologically.

Show me someone whose head is relatively still or focused on the hitting zone during and slightly after the hit, and most likely you are looking at a solid stroke which will hold up under pressure.

Follow-Through

Is the follow-through over the shoulder, or around the shoulder, or across the side? The answer is yes. It can be anyone of those. The follow-through isn't rigid. It's a function of the shot the player is trying to hit.

When the player is deeper in the court or trying to neutralize, the finish is going to be different from when he or she is hitting down the line on a short ball. With the grips in the modern game, players need to understand how to "work" the ball by turning over the hand and wrist in order to control the trajectory and spin on the shot.

For the full article, click HERE.