Many people think being a captain is ordering your team to do something or being the best on your team. But it's neither of those things. It's about knowing your team, working hard to set an example, being positive and encouraging, knowing yourself, communication, and having a strong mental game.
Know how your team plays. If they're sensitive, you probably shouldn't say anything too aggressive. Sometimes it's okay, as long as it's not constant. Knowing your teammates allows you to adapt to what to say/do. Knowing your teammates shows your team that you care about them and want the best for them.
Work hard and lead by example. The harder you work, the more other teammates will look up to you and want to be like you. It can be a lot of pressure, but it will improve your team and your own reputation. Sometimes teams will try to work as hard as the captain to look good. But some teams don't work that way, and they need encouragement and positive words.
Be positive and encourage your teammates. When you say, "Great job! Keep it up!" your team knows that you are paying attention and complimenting them. Getting a compliment releases dopamine, which feels nice, and they want more of that feeling, so they'd work hard and keep doing what they're doing or better.
Know yourself, and know what you want. You can't help other people if you don't even know yourself. Knowing yourself gives you the ability to be confident in your decisions. If you aren't confident the team will be hesitant to follow you. I know I would want a confident leader who cares about the team. I don't want a leader who doesn't know what they're doing and just screams at people to do better.
Communication. This one is a big one. Being able to communicate helps the team understand where you are coming from. Also, when you speak, the team knows the base one what communication is. This will help the team improve mentally.
Strong mental game. Having a strong mental game can help you and your team. If/when you get upset, you can somehow reset your mind to a positive mindset. I reset my mind by pulling up my socks. Come up with some sort of physical motion to reset your mind. When you have a solid mental game, you can be more positive and help your team with a clear mind.
These steps work for most sports. It doesn't have to be soccer. You don't have to be the best player, know more about the game, or be the most popular. Being strong and understanding the points covered above will help you be a great captain.