Ryan Hall talked about it on a podcast once, he said that focused repetitions are the key, you want to focus on how people are escaping that position and eliminate it. For example, if you're working half guard and people are getting through it with a back step pass, focus on shutting down that back step. Everything has a counter, find an attack to their counter and drill the heck out of it to the point where people think "Oh crap, if I back step here I'm getting swept for sure." Shut down every path one by one until there are no paths for them left.