<p>Since you're aiming at some very selective colleges, take a look at what Stanford says on its site: <a href="http://www.stanford.edu/dept/uga/criteria/index.html%5B/url%5D">http://www.stanford.edu/dept/uga/criteria/index.html</a></p>
<p>note in particular they say * we are interested in students who have made significant contributions to the life of their school or community. We do not favor one type of activity over another; nor is it necessary to participate in a large number of activities. Rather, we look for students who have committed themselves to their chosen activities over a period of time and who have shown energy and enthusiasm in working with others.*</p>
<p>In other words, don't join every club on campus; figure out what you like, then commit yourself to it. Push yourself to excel and win awards, to get leadership positions.</p>
<p>BTW you will also need strong recs, as well as great essays. So take the teachers at your school that have a reputation for being tough but really making students learn (both for your own personal benefit and for those recs), and while you don't want to be a brown-noser you do want to work hard and get noticed.</p>