how to find the right fraternities to rush?

You should look at their Facebook rush group from this past rush and get in contact with the rush chair, just letting them know your interested in rushing next semester. Its always good to be on a fraternity's radar before rush even starts. A lot of fraternities will invite prospective rushes to parties, day drinks etc during the semester just to get a head start on rush.

Also meet the greeks is a good way to get a first impression of many of the fraternities. Try to have a meaningful conversation with as many different frats as you can to try and feel out which ones you like. Don't just say "hi my name is ____" and put your name in their computer... you have to do something that stands out, hundreds of kids pass by every frat doing the same thing, what makes you better/different. From then you can narrow down the frats you like and attend their sober event and if you play your cards right you'll get invited to their rush parties/pregames/drinking events at night during rush week.