Shuffle your feet when moving. Know your opponents strengths and take them away. Force the weak hand. When you slide, do it under control. Slide body on body.
Communication is the key to good defense.
Who has the ball, who has the slide, etc. Take pride in the little things. Here's a few tips to make you into the human vacuum. Use the proper technique. Keep your body low to the ground and in between the ball and your opponent, keep your hand nearest the butt end of your stick down, explode through the ball, and immediately cradle and tuck your stick.