Advertising can be both a means of promotion and a revenue stream for a convention.
Things to consider:
- Size of audience
- Interest level of audience
- Breadth of audience
- Focus of audience (for instance, purchasing a mailing list from SFWA is often useful for putting together a programming mailing)
- Cost (in the case of ad trades, you may want to consider both your incremental cost and the opportunity cost)
Ads don't sell themselves. A well organized ad solicitation is critical. The most effective solicitation will mention a specific interest of the sales target. Look up your Guest of Honor on isfdb.org and solicit all of his or her publishers mentioning that you are highlighting the work of someone they publish. If you're feeling ambitious, do this for all of your program participants using a mail merge. Solicit nearby businesses that your attendees might patronize. Solicit every business you list in the restaurant guide. If your demographic includes a large concentration of people in a particular field, solicit employers in that field.
Pretty much any publication can take advertising. The Hugo Awards Ceremony program or a well-run souvenir book or restaurant guide can be entirely self-supporting or even an income center for the convention. Some publications (depending on your neighborhood, this might include the restaurant guide) are sufficiently optional that funding them solely from ad sales (no ads, no publication) is a reasonable approach. A small, at-con publication such as a newsletter or pocket program can only take a small amount of advertising, so fairness must be considered (no taking ads from only one Worldcon bidder, say) and rates set appropriately. Access to at-con publication advertising can be a good way to attract sponsorships or other package deals.
Some conventions ask for reciprocity for linking to other fan organizations on their web sites.
Systems like AdWords have recently made it practical for fan organizations to accept online advertising. Consider the impact advertisement placing, style, and content when deciding whether to do this.
Advertising-supported services such as Yahoo! Groups and Gmail are in common use by SF organizations.
It's easier to get sponsorship for some particular aspect of a convention than for the whole thing. Gaming companies sponsor gaming rooms, and fan organizations sponsor con suites (here you want to target the organization who has the money and interest but not the people to throw a room party). Companies that are there to hire like to sponsor events that relate to their company cultures in some way.
Sponsorship pricing is about figuring out the sponsoring organization's budget and putting together a package that gives them what they feel is good value for that money. Banners, print advertising, mentions in the convention blog, free memberships, and space for an event, display, or table are all good things to include in a package. Space in a convention hotel may be free for you but its value to a for-profit concern is about $1 per square foot. Don't be shy about putting cash values on the other things the organization gets.
When soliciting sponsorship, bear in mind who your competition is. Companies who are trying to hire hope to save $5000 or more in referral fees to headhunters and resume services. Gaming companies might be comparing you to the cost of a booth at an electronics show (at CES, booths start at $4000). Don't imagine that a sponsor is going to provide your entire budget.
Your organization might have other reasons for taking advertising than simply raising money. You might run a free ad for the next year's convention, for a charity you support, or for another organization with which you are friendly. You might give discounted rates to other fan organizations, to dealers who have purchased space at your convention, or to restaurants who are willing to provide a discount to your members. Be sure that the benefit (cash or otherwise) of accepting advertising is higher than the marginal cost of providing it. Pricing your advertising too cheaply can make businesses take you less seriously; demand is surprisingly inelastic.
Any deadline you give advertisers, they will miss. Many publications will need to know if the ad is coming before they need the ad itself and so separate reservation and copy deadlines will be useful. Deadlines too far after a solicitation is received reduce the urgency, but at the same time some potential advertisers (comic book publishers, for instance) have very long budget cycles; you may want to solicit in multiple waves. Arisia solicits three months out with a reservation deadline six weeks out; the real reservation deadline with Publications is four weeks out and drop-dead for copy is two weeks (since the printer is local; for a remote printer add two weeks to this schedule).
How is ad income budgeted? What happens in the case of an income shortfall or excess? The organization as a whole may be depending on the income, but making all ad income go to the bottom line means that the publication in which the ad appears must cut back on other content if more ads are sold than were budgeted. Who is selling the ads? Don't create a conflict of interest; your publication editor should be incented (or at least not disincented) to take advertising. At the same time, too much advertising can make a publication hard to use; make sure the ads you take support a net improvement in the publication.
Rush charges on printing are very expensive, so it's important to ensure that ad sales are cut off before they cause schedule overruns.