When shadowboxing, don't forget the otherguy. By that I mean keeping track of what your opponent would be seeing while you are punching away., or what you would be seeing were your opponent punching at you. The mirror is a great tool. Also what do you do to get in place to throw combinations- a feint, a slip or a parry? Is he punching in the middle of your sequences? These are the things that count. If at all possible look up a book called In This Corner by Peter Heller I think (help, somebody?) and read what Tommy Loughran has to say about training in general and shadow boxing in particular.