The forehand grip is mainly used for forehand overhead shots. It’s an easy grip to learn, and also provides a useful reference point for learning the other grips.
It’s like holding an axe
Imagine you are chopping wood with an axe. You wouldn’t chop with the axe at an angle; you would always have the blade pointing straight down. That is the correct angle for a forehand grip.
However, it’s not exactly like holding an axe. Your grip should be relaxed, not tight.
Alternatively: hold the racket head in your hand, then carefully slide your hand down the racket. Now wrap your fingers around the handle. This will also get you the correct angle.
Your fingers should make a V shape
The thumb and index finger should form a V shape, with the bottom of the V directly over the top bevel and in line with the racket head.
It’s important to have a sharp V shape, not a rounded U shape. If you have a U shape, it’s a sign that you’re gripping the racket incorrectly. It probably also means you are gripping too tight.
Placement of the thumb
Since this is a forehand grip, the thumb is placed in a way that’s suitable for playing forehand shots. That means only the side part of the thumb is touching the handle. The pad of the thumb is off the handle.
The thumb can be allowed to curl around the handle (that’s my personal preference), or you can hold it straight. In any case, the grip will change when you tighten it during the stroke.
Gaps between the fingers
Note that there are small gaps between the fingers. This is true for all the other grips too.
There is also a bigger gap between the index finger and the middle finger.
Index finger placement
The index finger wraps gently around the handle. It’s important that this finger is not straight. Pointing the index finger up the handle is a common error; not only is this very bad technique, but also it may cause injury.
Hold the racket lightly in the fingers, not in the palm
The racket should be cradled gently in the fingers, and not in the palm. You can check this by taking the thumb off the grip.
This is important, and applies to all the other grips too.