Be perceptive on defense. Get to know your opponent. Learn how your opponent operates and you'll learn how to diminish his or her effectiveness.
For example, is your opponent a "move player"?
Move players do things according to habit or involuntary reflex rather than choice. Consequently, they are prisoners of these habits — and you know how hard it is to break a habit!
Each move consists of a fake, that is, something which is not real, followed immediately by something real, a shot or drive.
For example, as soon as some right-handed move players receive a pass, they will fake a drive to the left and drive right, no matter what the opposing players or their teammates are doing.
Identify the moves of the player you are guarding. Then, take them away. You take the move away by ignoring the fake and being ready to stop the drive or shot. Another example of how move players are creatures of habit can be seen in some right-handed post players.
After receiving a pass with their backs to the basket, these players will show the ball as they turn their heads and shoulders to the right. Ignore this fake. Be ready for their quickly turning to their left and either going to the hoop or shooting.