how to get into top tier--

be rich and fake, mostly fake

Be a hot blonde cheerleader with good grades and a lot of money.

Just be yourself and hope for the best ;)

Pray to God.

As someone in a top tier who is neither blonde nor rich, I disagree with that stuff. Money does matter, but it's not so much "being rich" as it's about "being able to afford your dues." Sororities are expensive. Top tier sororities are often the most expensive (as they generally have houses / meal plans / etc.). No sorority, even the bottom tiers, want to waste their time or yours by offering you a bid and having you drop because you can't afford the dues. I'm my parents and I are not well off in the slightest but I do make enough financial aid to take care of my dues for me as well as my books and school needs. As long as you pay your dues, no one cares or hassles you about where you vacation or what brand clothing you wear (considering we all end up wearing sorority or frat shirts with leggings around campus 99% of the time anyway out of comfort).

The real way to go top tier
-be pretty. Sorry, that's a harsh pill to swallow, but that's the honest truth of it. Be attractive and you will do well in recruitment.
-have decent grades. You don't need to be a rocket scientist but many of the sororities have rules about what gpas they are allowed to take. Some sororities could want you super badly but if your gpa isn't up to scratch their organizations literally won't let them take you.
-don't be a total weirdo. We get hot girls come through all the time, but if talking to them is like talking to a wall or if you seem unfriendly, the sorority is gonna get bad vibes and drop you.