This is one of the most popular and commonly used grips for baseball. This falls under the category of breaking pitches. Grab the ball in such a manner that your middle finger touches the horseshoe part of the seam as it gets narrow. The index finger has to be just above the middle finger, side by side, and touching the white portion of leather. As you throw the ball, your wrist should be rotated towards the plate at the moment of release. This grip will impart the spin for a good curve to your pitch.
Three Finger Changeup
In this grip, your ring, middle, and index fingers should be centered on top of the ball. The thumb and the pinky finger have to be placed on the white leather beneath the ball. After that, the ball should be held deep in your palm for taking the speed off the pitch. The ball has to be thrown like a fastball, barring the exception happening at the last minute. That is, your elbow should lead your arm downwards, like you are pulling a shade or breaking a piece of chalk on a wall.
Four Seam Fastball
To begin with, put your index and middle fingertips on the horseshoe seam of the ball. The seam has to face into the ring finger. Follow that by placing your thumb exactly underneath the ball, resting it on the leather. It has to rest at the center of the seam. It is advisable not to grip the ball too tightly. Moreover, there has to be a little gap between your palm and the ball.
The grip for the slider pitch is seen to be as the best in baseball. The hitter can be dismissed from both sides of the plate with this grip. With your index and middle finger, grip the ball across its seam, at the point where it becomes the widest. These two fingers should be in the outer direction of the ball, just slightly. The thumb then goes under the ball, and the ring and pinkie fingers have to go on its side. Remember, none of them should make contact with the ball's surface. The pressure should be exerted with your thumb and middle finger when the ball is being released. You have to cut through the ball with the middle finger, unlike fastball. Otherwise, it resembles the fastball. Till the actual release, the fingers have to be on top of the ball. At that moment, turn the ball with your fingers.
This one is a combination of 2 different grips. It is an advanced variation of the curveball. It is thrown in the same manner as the curveball, just that, your finger should be tucked back in the seam of the ball. Your knuckles have to be in the direction of the target, rather than the index finger.
Keep practicing. That is the only way to get better at pitching.