There was a simple reason why montiel got clocked: He didn't move his head when he was punching. I'm sure you have all seen the video. Wide open, he wings a right hand, lands a glancing blow, and then stands there to be countered.
Something that I like to say a lot, and have said over and over, is that, in every element of your training you need to practice what you do after throwing punches. When you throw a right hand and the opponentgets outside of it, you need to get low. If he slips outside your right hand, and doesn't counter with a right, it has to be a left hook, and you need to get under it. These are things you train yourself to do, not only in sparring but in working the mitts and on the bags.
Another thing is moving your head when you punch, and I don't mean that Tyson/D'Amato nonsense of punching then wagging your head side-to-side four inches in either direction. What I mean is moving your head with your body. Properly thrown, after a right hand, the right shoulder protects your skull area from a left hook, and your head is out of the way of right hand counters. Take a look at Toney/McCallum 1 and 2, and watch Toney avoid counters to his right hand.