I'm kind of rambling here just writing stuff as it comes to mind.
We've done tons of shows. Indoors, outdoors, strictly bikes shows, car shows, festivals, history events and many others. We're part of a car show this weekend.
Think of a catchy name for the event. Set up a website or blog for the event and of course a Facebook page. Don't only do Facebook. Make and print posters and distribute them.
Doing just a simple show is well... just that... simple. Set up bikes and look at them. Make sure people have a proper way to stand their bike. Something to display information of the bike is always nice. A sheet of paper or an index card in the spokes.
Will you supply food and drink?
You want to do indoor or outdoor? Getting an indoor venue can be difficult and expensive. Outdoor a lot easier. Reserve a space at a park or team up with a bike shop or other store and use their lot. Hook up with an art gallery.
Would you like to do more than just the show i.e. games or contests? Do you want voting on or judging of the bikes?
If you're wanting a show where people bring out as many of their bikes as they can I wouldn't combine it with a ride or swap.
There can be legal issues depending on where you have it and what you're doing. Having just strictly a show (display of bikes) probably the best way to avoid any legal/liability problems.
Can you think of some specific questions it might be a little easier to help?
Maybe you can get some ideas from our website.
This link will take you to multiple pages of shows we've done
http://locojoe.com/coasters/plugin/tag/show
This one on our big festival
http://locojoe.com/coasters/plugin/tag/bike+fest