Passion. Your activities are supposed to be a reflection of you and what you care about. Admissions officers can usually tell when you're just doing activities to pad out your resume. Colleges love students who are passionate because, more often than not, they are the ones who will stick with something through thick and thin and go on to change the world. You can show passion by focusing on a couple activities and dedicating a significant amount of time to them.
Leadership. Leaders are the people who will be at the forefront of change and the first to take on new challenges. Since colleges are looking to educate and shape the leaders of tomorrow, they love to see students who are taking initiative to be leaders through their extracurricular activities. You can do this by leading a group or activity, being in charge of a project, or otherwise motivating or directing other students.
Impact. How have you changed your activity for the better? Have you expanded membership or the amount of activities your extracurricular does? If you saw a problem, did you fix it? Once again, colleges are looking for the people who are going to change the world someday. In your activities, you can show them that you're the type of person who takes something and leaves it better than you found it.