Hi there!
I too am a member of a specific kind of GLO, though mine is for girls in music. We have trouble getting members, but here's some things that really help.
Get your letters out there whenever possible! Make big cutout letters that say your sorority's name and tape them up in the engineering building. Wear your letters as much as possible.
Also, ask the dean if you can have one of the bulliten boards in the building only to be used by your sorority. We have one, and we decorate it monthly with SAI-related stuff. You can use this board to put up information, pictures, etc about your sorority so passersby can stop and read all about you!
When it comes close to time for rush/recruitment activities, post signs, posters, banners etc for it everywhere you can, and hand out invitations, etc.
Be as visible as possible, and talk to all the qualified girls as you can.
Hope this helps!