Seriously Jeff it isn't very hard. Get a job, and become an assistant manager. I work at Quiznos, and im a closing manager. Colleges ask me about my leadership experience, and then i ask them if they've ever had to convince 3 lazy people every night to work. If you dont need a job then go volunteer at something for a few hours a week. If you dont want to help people then get majorly involved in a club. Becoming an officer of a club gives you something to do, looks great for college, its fun, and you get to hang out with friends. There is no best thing for a college application. The college application is a combination of basically your highschool life. Its having good grades, good scores, leadership skills, and showing that your not antisocial. They want to know you are going to some how give a positive contribution to their college.
2ndly for anyone who said you dont learn anything when you volunteer, that is complete nonsense. It depends where you volunteer at. Dont generalize volunteering based off one of your personal experiences where you didnt learn anything. Volunteer at a hospital, im sure you will learn something. You can volunteer at a homeless shelter, and im sure you'll learn something; you might learn somethign about yourself or just about other people, but you wont leave without some type of added knowledge.