Man on Man

I'm 5'11" tall and 168lbs. I wanted to know how do you catch up your man with out going behind your man's back while I am defending. I averaged 2 blocks/ 2steals 10\' season. 19 mins per game. I don\'t shoot much but I have strong defense. Help on screen man on man? Suppose I am defending a player and then he went through screen, I end up getting behind his back and unable to catch up on him because he caught the ball and shoot.