The larger the event, the earlier you should promote it. If you would like the big names to attend your event, then you have to remember, these are busy people and sometimes their calendars are filling up 12-24 months in advance. So a few things to consider when you are organising your event:

1. It's all about timing: Make sure your event does not clash with any other significant events in your area at the same time, and preferably not within the same 3 week window (a week either side of your event).
2. Remove the marketing confusion: Make sure your event does not coincide with your competitor's events. You don't want your message to get confused with theirs.
3. Viral marketing and word of mouth: Are your events the "go to" event of the year? Do you want them to be even though you haven't quite got that stature in the marketplace yet? It is important to establish your credibility in the marketplace and social networks are no different. It takes time to build a following and it takes something memorable and newsworthy for it to be considered good enough to be passed on and passed forward. One thing the social networkers hate is organisations who think they can join the networks and start bombarding the scene with the same spammy messages over and over and over again. Believe me when I say this - you will lose both your following and your credibility as a result.
4. Do not neglect the hard copy brochures: When it comes to large and expensive events - people still like to receive something tangible in the mail. But brochures should go hand in hand with your online presence. Not only the social networks, but emails and websites should all be branded in similar fashion.