A few things:
You should focus more on "recruitment" and less on "rush," meaning you should be utilizing and motivating all of your members to make connections with people year-long. Don't worry about big events, they mean bigger effort and bigger disappointment if they don't work out. Have your members reach out to people in their classes, their dorm, and other organizations they belong to. Build friendships with these people and introduce them to other brothers. A 2:1 brother-potential ratio is a good starting point - go out to lunch, study together, etc. Bring them into your circle of friends and then bring up the idea of being in a fraternity. At this point they're already friends with you and will want to be a part of ZBT.
Also see these threads:
http://www.greekchat.com/gcforums/sh...d.php?t=107222
http://www.greekchat.com/gcforums/sh...d.php?t=100682
http://www.greekchat.com/gcforums/sh...d.php?t=105943
http://www.greekchat.com/gcforums/sh...d.php?t=107740
The
Phired Up Blog is another great resource.
Good luck!