Assuming your form is otherwise perfect, your drop, change up and rise are already dialed and you're looking for a pitch to add to your repertoire, then it is time to start working on a curve. In case you didn't notice, I REALLY encourage kids to learn a drop/fastball, change then rise as their primary pitches, then use the curve to keep the batter guessing. Many times, a rise grip and feel can easily be converted to a curve. A pitching coach and 1:1 instruction makes the whole process much easier.

There are probably four common grips for throwing a curve. Regardless of the grip and technique, the bottom line is that the ball needs to spin with an axis that is as perpendicular to the target as possible. Many people throw a ball that has some spiral spin and moves a little, so they call it a curve.

My favorite grip is similar to a four-seam fastball grip with the fingers on the top of the backwards "C," but the middle finger moves next to the index finger. The palm cups upward toward the sky and slightly towards second base, and the back of the hand facing the ground and slightly towards home plate. The pinky knuckle leads the way and the finger tips pull the outside of the ball around towards the target. The result is a slightly off-side speed pitch with a very flat spin and a perpendicular axis. I believe this grip/technique provides the most movement, but if you ask/look around, you will find there is almost a Ford/Chevy/Dodge deal going on depending on who you talk to!

Another grip I like is identical to a 4 seam fast/drop ball, but putting the index and middle finger tips on the top seam of the regular "C." The back of the hand/pinky still leads the way on the down swing. At release, the hand rotates on the wrist towards the target and the middle finger pulls on the seam towards the palm. The palm is also less cupped upward and the fingertips are more on the bottom of the ball and the thumb on the top.

The best way is to experiment with a striped or other wise marked ball and a catcher. A grip/technique that moves the most from the catcher's perspective is probably the one to stick with.

Have fun!