Many pitchers will experience early success based solely on their ability to locate their fastball. However, regardless of a pitcher's velocity or his command, eventually he'll need to develop secondary pitches to keep hitters guessing and off-balance. The first off-speed pitch that is introduced to a young pitcher should undoubtedly be the change-up.
The change-up is a safer pitch for young players to throw, as opposed to a slider or curve, and is an effective one for them to use. It's an off-speed pitch that's 8-to-10 mph slower than the fastball, carrying a little more velocity than a batting practice fastball. But it's delivered with the same arm speed and action as a fastball, so the batter starts his swing early, reducing his power. The key is arm speed and aggressiveness with the change-up. If the hitters usually see fastball out of the hand the change equalizes or stops bat speed.
Since the pitches are delivered with the same approach, the key difference is in the grip, which changes the speed. The change-up is thrown with the same arm speed of a fastball, but the ball is released off the second row of the knuckles rather than the fingertips. The hand is behind the ball and your fingers should be on top the ball before release. Release the pitch out front with good extension and you should feel the ball come off your fingertips.
While not the only change-up grip, the circle-change is one of the more popular change-ups and is frequently used by younger pitchers. It's gripped with the index finger tucked against the thumb. The ring and middle fingers are along the seams. The ball slides off those fingers, with the force directed alongside the ball, which takes something off the pitch. As you gain more feel and confidence with the change-up, you can apply pressure with your fingers to take more velocity off the pitch, creating more deception.
With a four-seam circle-change, the middle and ring fingers are across the four seams. The thumb and index finger touch to form a circle on the side of the ball. This pitch produces more backspin than others. It looks like a four-seam fastball but is slower. You should use the grip if you primarily throw a four-seam fastball. You want the change up to look like your fastball.
Many pitchers, such as the ageless Jamie Moyer, enjoyed long careers with little more than an effective change-up to complement a mid-80s fastball. They keep batters off balance by constantly changing the speeds of their pitches. The change-up is the toughest pitch for hitters to recognize the seams or rotation visually. Curt Shilling, one of the greatest postseason pitchers of all time, didn't even attempt to throw a curveball until he was 18 years old and did not throw one in the Major Leagues.
You should throw the change-up daily in your regular catch routine. Increasing the feel and comfort of the pitch will increase your confidence in the pitch. Always have a mindset of attack or aggression, instead of slowed down and passive.