How do I get into a top tier sorority?
It depends on the school but you’re going to find better advice about going through recruitment on the total sorority move website, the greek rank website, the her campus website, and the sorority sugar website. Mostly what people are going to tell you though is if you’re simply trying to get into a top tier sorority, you’re going through recruitment for the wrong reasons and you aren’t going to find find a sisterhood that you truly fit with.
I sent you a PM. Based on former threads you’ve created, it doesn’t look like you are going to any of the schools with really competitive formal recruitment. So you may not needs recs and all that.
I agree, though, that keeping an open mind during the rush process is probably the best thing you can do. The most common reason young women don’t match at any sorority - even at many competitive schools - is they cut too many houses too early in an effort to only try to get a bid to specific houses. I’ve heard lots of recruitment counselors and Greek women say time and time again that the houses you expect to be your favorites going in may turn out not to be the ones that are your favorites coming out.
(This is, of course, assuming that you are interested in NPC sororities. If you are interested in NPHC, NALFO or other multicultural sororities - that’s a whole other kettle of fish.)
Get good letters of recommendation from alumni.
All replies are spot on. Going through recruitment isn’t about saying oh I wanna be at this sorority or this one. Its a process where you want to be with people who you will click with. You don’t want to be fake to yourself. Top-Tier sororities also depend at the school. At my school Kappa Delta would be at the top where as at my friend’s college, its one of the lower-tiers there. It all depends honestly. The main thing is if you are yourself you’ll be happy at anyone you get a bid too. I recommend checking out Sorority Sugar on Tumblr. Some of the stuff is tailored for rush at bigger SEC schools, but a lot of it can be used for anyone going through recruitment. As for letters of recs, really only huge schools require them. I know mine wouldn’t even take them, so it depends where you go. If you have any questions feel free to PM me! 
Good luck!
Why gamble? Go ahead and get some recs. Ask among your mom’s friends (or ask her to) to find who are sorority alumnae of the sororities at your school. They don’t have to graduates of your school, just members of those sororities. Ask among teachers, yes all the way back to elementary. Neighbors, your parents’ co-workers, people at church, where you work…and once you find an alum, ask if she knows alums in other sororities.
Once you find alumnae and they agree to write a rec, have a packet prepared to hand to them with your resume, a transcript, and a photo. That will give them everything they need for writing a rec. You wouldn’t go into a test without studying. Why go through sorority recruitment without preparing?