A promotional party or event is mainly a marketing and public relations tool to drum up interest for a product, service or some other type of business. Promotional parties can run the gamut from trendy to highbrow to grunge. The key to the party is having it both appeal to the audience that you are hoping to attract and pushing the product in a way that creates interest.
Appeal to the Market's Tastes
A promotional event is nothing if no one shows up or leaves early because they don't like what they find. To get people in the door, and to get them to stay once they are there, you need to give them something they want. If you study your target audience, you should be able to learn what things will most likely appeal to them. For example, provide live music--but be careful whom you choose to provide it. A band covering classic rocks songs, for example, would create quite a different mood and atmosphere than, say, a small jazz combo.
Offer Free Stuff
From free food and drinks to free branded items, such as water bottles or key chains to a raffle-style drawing, free items, or the possibility of free items, will bring people to your event, or can at least entice them if they are still trying to decide whether or not they want to go. "Brand" anything that you give out; that is, make sure the items have your company's name, logo and general contact information on them.
Provide Ways for Attendees to Get Involved
To make the experience better for your attendees, and to make them more likely to talk about it afterward, include ways for people to get involved in the event happening around them. From drawings on the half hour to a face painting station at a family event, to the opportunity to try something out that is related to the thing that you are promoting, such as including a rock climbing wall at a rock climbing event, getting people actively involved will make the event more memorable to them.