People are constantly asking me for advice on how to get promoted. They want to move up the ranks at their company, take on more responsibly, and expand their sphere of influence. While the notion of being a leader seems nice (but possibly far off), you've got it backward. It's not that you're anointed leader and with that suddenly bestowed with responsibility--quite the opposite, actually. If you want to become a leader, start acting like one now.
Leadership isn't about your title, nor is it about bossing others around. Being a strong leader means thinking about the team's needs before your own, helping other people to grow and maximize their own full potential, and sharing credit when it's due (don't forget shouldering blame as needed, too). Why do you need to wait to get a promotion to start doing any of this? Instead, begin today. The more qualities of a leader that you exhibit, the more obvious a choice you'll be for the actual promotion down the road. By positioning yourself as someone who's ready to take on more, you'll be hard to ignore.
Let's say you're a salesperson striving to be a sales manager. While it would be inappropriate to ask your peer-level colleagues for their numbers or hold them accountable to a certain quota, you certainly can act in a way that helps enable their success. For example, if a teammate struggled with his last demo, ask if he wants to shadow you on a few sales calls and then have a discussion over lunch about what went well and what didn't so you can help him improve his game.
If it's the end of the month and you know the crew will be there working late each day, be the one to show up with snacks and some music--by boosting morale and encouraging others to give all they have, you've helped the greater good. If you lose a big client and your current manager asks the group what went wrong, be the first person to vocalize how you personally could have done better--without casting fault toward anyone else. Or, if a big win unfolds, be the first to talk about what an awesome job others delivered on a particular project. By giving praise to a teammate, or shouldering a difficult burden, you're positioning yourself as the obvious choice for leadership. Leadership is a state of mind rather than a position of authority. Make a commitment to help others achieve more, and a leader you become.
If you start acting like one, you're already a leader. With or without the fancy title.