Although leadership is a complex subject, the approach to developing leadership can be simplified by focusing on two key components: listening and decision-making.
Listening by itself won't necessarily make you a better leader, but it will make you a better person. If you listen, that means you are tolerant of the other person and open-minded enough to accept new ideas. It also builds trust by simply being there for them.
Through developing leadership you develop relationships - and vice versa.
Decision-making is what separates a good leader from a bad leader. If you make consistently better decisions than your followers would make - then they have a reason to keep following you. (Let's face it: making decisions is a big burden. A good leader makes life much easier for everyone.)
Developing leadership can be an arduous process, but can also be made easier if you maintain honesty and are courageous enough to say 'I don't know' when you don't know something.