This advice can be applied to any vendor event—craft show, home and garden show, etc.—but for now I will make it specific to book signing events.
Did you get that? No, that's not a spot for someone to advertise on my blog. It's telling you that you need to advertise the HELL out of your event from 3-6 months in advance.
I've been to over 20 book signing events in the past year, and it amazes me how much effort the organizers will put into things like event applications, event passes, online booth graphics, parking passes, etc., but do a horrible job of getting the word out. I know they mean well, but there we sit, our beautiful tables flanked with our goods....waiting for people to show.
It's not enough to advertise online, though you should definitely have a Facebook page dedicated to your event. Or, if you already have a group with many followers, create the Event on that page. Encourage people to share it. If your group is a Closed Group, then those in that group can't share things to their friends unless they copy and paste the links. Therefore, a Facebook Page is the best bet. Don't forget Twitter as well.
I see a lot of events that only use online event listers like Eventbrite. When is the last time you went to Eventbrite to see what's happening in your town? Exactly. Some online news media pair up with Eventbrite, but it's still not enough. Do it, but do more.
I recently asked an event coordinator where they are advertising, and you should too. They mentioned a few of their local papers...in their town of 12,000. Wow. If you have an upcoming event, pick the largest city near you and get it in their newspaper. Many times it's free. Search "Local Events" or "What's Happening Around Town?" or "Things To Do" and post your ad there weeks in advance.
And finally, hand out flyers at your local church, book clubs, author groups, and other book signing events to help spread the word. You want to reach both authors AND readers. Have an online pdf flyer that authors can print and give out at their signing events to encourage patrons to attend yours.
Got you there, didn't I? Check around to see what other events are planned for a weekend before you schedule your event. Don't pick a day when the largest craft show or book signing event in the state's history happens to fall on the weekend you have in mind. Sure enough, you will hear crickets.