See also Hosting a Write-a-thon
An edit party can be a great way to build the content of your wiki, have fun by introducing editors to each other, and recruit new users and editors. The basic idea is simple - get some people together to work on the wiki together. Here are some ideas for making your edit party successful - add your own ideas, too! Keep in mind that the edit party should be pretty simple - if you're being held back by too many details to plan, you should probably stop planning and just go out and have your edit party. That said, these are some things you may want to consider.
Where to have the party
Public libraries are great places because lots of people come and go, and there are often computers available. You should probably talk to the library to ask if they want to partner with you - they're usually interested in becoming hubs of community involvement, and they may even be interested in adopting the wiki as a project of theirs.
Cafes can also be nice - people come and go frequently, and the cafe will probably be happy to have you bringing people in (as long as you buy something when you're there). Be sure to pick one with wireless internet, of course. You may have to lend people your laptop, since not everyone comes to a cafe with a laptop, so be ready to read a book or do something else while your computer is in use.
When picking a space it's important to consider who might feel comfortable attending. For instance, in the early days of a project it may not matter that you're having editing meetups at someone's house (it's easy and cheap!). As the project progresses -- and you'd like people you've never met to attend -- showing up at a stranger's house can be intimidating. Similarly, cafes and libraries both attract different crowds. Attending an event at a library may seem like an overly civic-minded task, and many younger, not traditionally civically-involved people may not ever attend library-based events. Cafes bring their own problems -- noise, sometimes a lack of space, lack of dedicated rooms and the expectation that you buy something.
What to bring to the party
Bring your laptop, of course. If you can print up some fliers to bring, you can pass them out to people you talk to about the wiki.
If you can manage to arrange any food and/or drink to share, you'll attract more people, and people will be more likely to come back.
Getting the word out about the party
Don't stress about this, since you can always talk to people at the party location, but if you want to try to get some extra people to come, start by contacting regular editors of your wiki (if there are any) - they'll probably continue to be your strongest editors. Post about the party on any community event calendars, and ask the venue you'll be hosting at if they're interested in promoting the event, or if they have suggestions for getting the word out.
What to do at the party
Encourage people to make pages about whatever they know about and are excited about. You don't need to stress out about trying to fill certain gaps in the wiki's content - your goal here is to build a community of people who enjoy building on the wiki, and you'll do that best if people write about whatever they want to write. Your role will probably be to float around and provide advice/troubleshooting - show people how to create links, and where they should be linking to their pages from, how to upload pictures, etc.
Feel free to reach out to people who walk by or are sitting nearby to encourage them to get involved. If you have a big poster or fliers up, it will help people see what you're about even without you reaching out to them.