Ditto to what everyone else said....advertising your letters is the key!
Also, get your sisters out there and involved. Have them participate in every aspect of campus life...if pledging freshman is your main focus, this is important, as freshman are really eager to take part in campus life. Make it so people say, "Gee, you can't walk anywhere without tripping over a Nu Sigma Chi!"
I know I might sound like Captain Obvious on this one, but make sure your sisters seem like they like each other on campus. Believe it or not, but PNMs notice if two sisters walk by each other without even a hello.
Good luck to you!
