1. Solve problems. Look around and find ways to make the world a better place. Observe your surroundings and listen to people. How can you help?
Discover what your talents are, develop them, and focus on applying them towards making a difference. Think of problems in the broader sense - they're not always easy to define.
Look for needs, niches, conflicts, gaps that need to be filled, and inefficiencies. The solutions won't always be creative or cutting edge; sometimes they're the simplest things.
2. Think of the big picture. As you're solving problems, you might notice patterns, and wonder if many of those problems are symptoms of a deeper, bigger problem. Thoreau once said, "For every thousand hacking at the leaves of evil, one is hacking at the root." Take a step back and try to find the root. The deeper problem is often not something anybody can solve alone; it'll require a group effort, which is where your role as a leader comes into play.
3. Be proactive. If you've got these ideas in your mind about what the deeper issues are, you can probably predict the problems that'll crop up as a result. Instead of waiting for those problems to appear, take steps to prevent them. If you can't prevent them, then you can at least prepare. That's the core difference between a leader and a manager. A good manager responds well to a variety of situations; a good leader takes effective action to prevent and create situations before they actually happen.
4. Make decisions, and take responsibility for the consequences. In order to exert influence and tackle bigger problems, you're going to need decision-making power, and those decisions will affect the people who grant you that power....