To develop leadership skills you need to put yourself in situations that give you leadership opportunities! Join a club, get a job, get involved in activities in your community. Any regularly-meeting social gathering is bound to have different offices that you can run for.
Another aspect about leadership that you can work on developing by yourself is self confidence. Self confidence is very important if you want to be a leader. If your leader isn't confident in themselves would you really trust them to lead you? One way that you can work on this is to research different exercises that will build your self confidence. One famous one is standing in the "Superman" pose. You stand straight and tall, chest out, hands at ninety-degree angles on your hips. This stance has been scientifically proven to increase one's feeling of confidence and self assurance.
Another aspect of good leadership is oration. What I mean by that is, to be able to lead people you need to be able to talk to them. One way I honed this skill in myself was to watch famous speeches. Notice what the speaker is doing that is making the speech so interesting, so dynamic. See if you can pick up habits in your own speech and develop your leadership voice.
That's all I can think of for now, but if you have more questions about this topic feel free to reach out to me, I'd love to help you further!