First, understand the difference between being a boss and being a leader (see above). You have to make a conscious choice to be a leader, and do things and exhibit traits that will encourage people to follow you. Just choosing to lead is a great first step!
To be a leader, you need people to follow. As a kid, when you’d play follow the leader, the game never really worked unless you could persuade your parents, siblings, and friends to stop what they were doing, get up, and follow you wherever you chose to go. Same holds true today. If you’re not an inspiring, trustworthy, competent, and confident person with a vision for the future, why should anyone follow you? Be the person others choose to follow. Give them a reason to do what you say or ask of them, and for them to want you to encourage them on their career path. The specifics of this depend, though, on your personality style, the situation, and the people you’re working with.
Clear communication with a vision for the future is essential. It’s hard to get up and follow people, even those you trust implicitly, when you don’t know where they’re going. Give people an idea of the end result, and they’ll be much more willing to come with you—especially if you give them leeway to make their own path, a reason for them to follow (what’s in it for me?), and encouragement along the way.
Recognizing efforts big and small, acting with compassion, and setting a good example as well as a good pace, goes a long way. Everyone likes to work with kind people and to know that their efforts are appreciated.
One last tip: Find a person you think is a great leader, then study his or her habits. What traits, characteristics, work styles, methods, and so on, does that person possess or employ that seem to work? What does this person’s followers say about him or her? What could you emulate?