ASAP. If you're a Sr in highschool, now is a good time to start looking. Make up a resume, and figure out who you're going to ask to send them. Get them everything they need (address where they need to send them, all of your personal info they need, and it probably wouldn't hurt if the sororties have their rec forms on the website to print one out and give it to them as well - whatever you can do to make their job easier). Remember, they're probably very busy women, and the more lead time you can give them, the better.
And don't forget the thank you cards.
