For a non-profit organization marketing an event could be a serious challenge. Lack of money and professional resources are very often the reasons to keep costs to a minimum while maximizing attendance, especially if it’s a fundraising activity.
You are probably busy and short on staff but if you care about your cashflow your event marketing should be a primary concern and the single most important part of your event. If no one shows up, it doesn’t matter how nice the catering looks.
Leveraging social media such as Facebook and Twitter are excellent and cost effective tools for event marketing. Your members, clients and friends have well-developed networks so you can get a lot of exposure for very little or no cost.
Contacting your local media seems like an obvious option, but very often non-profit organizations neglect it. Call all the papers, Radio and TV stations, their presence there could really boost attendance. There is a high probability that the people who attended your last event will come to your next event, so sending them personalized invitations.