What would you say is the most important aspect of being an NCO?

My personnal stand is to try do your best as a leader. Do your best to be tactically and technically sound in all you do. If you don't know an answer for what ever reason at least know where to get it. Keep in mind right now we have alot of hardened veterans that can run circles around most on the battlefield and can bring their troopers home in one piece (most of the time). Unfortunately they can't take care of those same troopers on the admin side of being a NCO. Taking care of our Soldiers is second only to mission and one aspect of that is mentoring. Providing them with the knowledge and skills to succeed in their military careers is our charge. I know this is a bit long but the answer isn't an easy one. My advice to any young NCO is learn from the examples of your previous leaders whether good or bad and use it in your tool bag to help develop your leadership style.

Instilling discipline and standards within the ranks, setting the example of excellence, and developing junior officers.

Training the Soldier to be better than you when they make it to your current rank.