Sign up to be a camp counselor. Some programs are very intensive and even give you leadership classes before you begin your stint as a counselor. Not only will this give you leadership experience from counseling and mentoring younger students, but it will give you leadership education as well. You can then apply this newfound knowledge to other areas and gain even more leadership experience.
Run for class president or student body president. Leading your entire class or school looks good on a college application. Not only does it give you proven leadership experience, but the fact that your entire body of peers came together and chose you to lead them is hard to ignore. It shows that you can garner trust and respect from your peers, making you an asset to any school.
Raise money through a fundraiser for your favorite cause or even start a nonprofit organization. Bringing a group of people together and inspiring them to work as a team to achieve a goal is an admirable quality in a leader. Colleges are looking for people who can inspire their peers to work together, come together as a community and strive harder towards their personal endeavors. If you can inspire your peers, it is another asset for the school.
Join school clubs. This is a way for any student to get leadership experience, especially if the club is devoted to a cause. You don't have to be elected by anyone and there are usually many experiences to choose from. If you can become the president of the club you join, that will look even better. Being in a club means working with others and sharing ideas, which is good experience for any potential leader. It can also include community involvement, which counts as leadership experience.
Be a student counselor. The ability to mentor your own peers and help them make good decisions is important leadership experience and something that colleges will look favorably upon. This is another position that shows that you are respected and trusted by your peers.