conference promotion tips?

I'm helping our Events department with their conference promotions and I'm trying to get some good tips for promoting their conferences.  The ones we do in the U.S. is good, but the ones for APAC and Europe needs a lot of help. We've done a lot of email promotions and it doesn't seem to help in generating registrations, and I'm not sure what they are doing with lead generation.  Promoting in LinkedIn is one thing we're looking into, and I'm looking into adroll or retargeting, and at least creating a buzz about the events on Twitter.  Any suggestions? Which ones are not worth trying?