When I think of a good captain ...the things that come to mind are:
1. Poise - Dont lose your cool, keep your head up and dont take sides in team sqaubles,calm the situation and let the coach sort it out for themselves.
2. Postive - Keep a positive, yet comeptitive attitude. In other words, stay upbeat and encourage teammates ..but dont pretend all is ok after taking an 11-0 whipping.
3. Lead by example - Do the simple (often overlooked things) everything from... being on time, to running out popouts, to wearing uni properly, to raking the field w/o coaxing.
I have 1 "Don't" ...
Don't repeat or reiterate everything the coach says, especially right after they say it ... or after a coach says something say "Yeah, Guys, C'mon" etc. etc. This typically breeds negative sentiment because the other kids think the captain is brown-nosing or trying to be in an authority position like a coach, when they are still a teammate. If the coach said it, its been said...the captain is not a coach (except for situatinal situations ON the field).
Thats my best shot at the attributes of a captain. Hope I helped, I am sure many other knowledgable folks will have good stuff to add.
Congrats!