Practice hitting curve balls a lot. Look for the spin.

It's difficult for many young players, but picking up the spin of the ball can tell you what type of pitch is being thrown. Curve ball always sping toward the batter, fastballs spin back toward the pitcher. Also by watching the wrist, if you can see the whole wrist (put your palm toward the hitter, we call this fat wrist) it's a fastball or maybe change, then turn palm so your thumb is facing toward your shoulder (skinny wrist) it's most likely a curve ball.