In addition to the the link KSUViolet06 posted, you might want to read through the different threads in the Recruitment forums.

If and when you are accepted, start contacting the women who will write recs for you early so you're not rushing at the last minute. If you don't know anyone, visit www.npcwomen.org to get more info on the Alumnae Panhellenic nearest you. In addition to that, ask those around you if they're sorority members.

Most important, keep your grades up, stay involved with your HS activities, have fun, and enjoy your senior year.