Make the players around you better. You do this by doing all of the earlier key points and encouraging your teammates
There are different types of leaders but I believe the best know how to lead by example, communicate well and when they give you a compliment you feel taller and stronger. In this OSA video are key points that I believe make a great captain. I'm sure there are more so please feel free to post your opinions in the comments about what you think makes a great captain.
#1. Lead by example. If your teammates see you being positive and working hard, they will follow suit.
#2. Be encouraging and positive when teammates mess up. If someone makes a mistake be the first to say "Keep your head up buddy. We all mess up. We trust you, just get back on defense". Don't yell at players for messing up.