If you think you're opponent may try to take you down, don't over commit to your punches. Throw 2-3 punches and back off. If you get to a point where you're moving in on your opponent throwing punches, he'll move back for 2-3 steps, stop, level change, and shoot . You will be coming into him, unable to stop your forward motion because you over commited. (I love it when that happens
Watch Chuck Liddel fight, he's a master of this. He never pursues his opponents until after he's landed the big punch and his opponent reeling.