Durendal

I know this an ancient thread, but I think the most important element of shadow boxing, while it's been mentioned that you have the luxury of slowing things down and envisioning an opponent, is stringing together combinations of attacks while shifting off lines. It's easy to just throw 1-2 or 1-2-3 combinations and say "that was a good shadow boxing warmup", but if you fight any experienced fighter with simple 1-2, 1-2 combos, they'll easily break you down. Shadow boxing is a great time to be a little more thoughtful (as being too thoughtful in a ring will get you knocked out). For me, shadow boxing is the time to string together 1-2-3-4-5-6-7-8-9 attacks while being able to shift around the opponent, break him down so that no matter who I'm fighting, even if in the ring he moves differently than I envisioned him moving while shadow boxing, by the time I hit with that 5th attack, he's gone no matter what, and if not, I can still move all around and bombard him with attacks with ease, while keeping good form and myself protected. It's basically training your muscle memory with good form so that you're ready for a real fight.