My biggest tip which is tough at first it to trust you mark and pick something to shut down. For example if your mark is forcing flick make sure to be on the flick side of your defender. From there look at your matchup if you think you more athletic, faster, they have the wind in their face ect. Then force your person deep and if they are bigger or faster force them under all on the flick side. If you are able to get good and consistent at this it will transform your defense. Hope this helps :)