Everyone has said wonderful things and I completely agree with everyone.
That being said, I would like to add that you have to be the epitome of the perfect band student. You are a student extension of your director. NEVER undermine a decision or action of your band director. Not in front of your band, not in front of a select group of friends, NEVER. If you disagree with something your director has done, bring it up with him in private, just the two of you. Nothing can be more destructive to your rehearsal or your band's preception of your director than a drum major who is on a different page than the director, because your attitude helps to determine the band's attitude.
Think about it, when the director is in a bad mood during rehearsal, are you or the rest of the band in a good mood? No. 95% of the time, the band's attitude reflects his. This also applies to you.
If you have any more questions, I would suggest purchasing a copy of The Dynamic Drum Major. This the text used as supplemental material for the George N. Parks Drum Major Academy. (George Parks is considered the expert on drum majoring around the country.) This book will answer any questions you will have concerning the position and any situation that comes with it.
I hope my comments have been helpful and best of luck in the future!