spring rush

You are better off waiting until formal recruitment in the fall. You will have more options then. Keep your grades up, get involved in a campus activity, get recs, get to know actives in houses.

Spring rush typically involves just a few sororities. You sign up with Panhellenic, and then wait for them to call you. They might ask you for for lunch, or to watch a TV show, or meet for coffee. It's all very low key. After two or three visits, you may or may not get a bid.
There's no big announcement, no big party or anything.
Despite what they say, sometimes the most popular groups do pledge new members in spring - they just already know who they want.

Why not? You don't have to pledge anywhere, and you'll meet some of the sorority girls. Or, you may very well find yourself a home.
Sign up right after Christmas break.

For many of the sororities who rush in the spring, you need to know sisters. Right after Christmas break, ask your friends who are in sororities if their house is participating in spring recruitment and if so, if they could put your name on the invite list to any events they are holding. Some events are informal (invite to lunch at the house) while other events are more organized (several PNMs invited to an evening get together with sisters). Good Luck!