I'll walk you through how I got 300 members in the matter of three days. I'm tired so I'll make it a simple short guide.
We'll be using a guild requiter addon as well as a simple keyspam program.
Step 1: Download and configure SuperGuildInvite to your liking, you can add a personal whisper if you'd like to.
SuperGuildInvite - Guild - World of Warcraft Addons - Curse
Step 2: Download or start up your keyspam program, I'll be using prospector.
http://www.ownedcore.com/forums/worl...ng-helper.html (Gemmore - A Free Prospecting Helper)
Step 3: Create a macro with this in it: /click SGI_InviteButton (Credit to frisko). Put your macro on to your bar.
Step 4: Start up WoW click your little SuperGuildInvite button press superscan and start up your keyspam program and configure it to spam your macro.
Edit: The guide has been changed since frisko gave us the macro. The version I originally used was to use a click spammer and put the cursor over the invite button. But that could not be run in the background as a keyspammer can.