Years ago, to promote my Charity Dinner I would drive around with posters pinning them to notice boards and leaving them in receptions of local companies. The poster was either unprofessional because it was printed at home or expensive if we had one done professionally.
Today things are so much easier! Social media including Facebook, Twitter and LinkedIn are by far the cheapest and quickest ways to get the message out about your event. There are a few things that will save you time before you get started: