I would suggest calling ahead of time to see if the dealer is pre-booking rides, or if it is first come-first serve basis.
If they are doing first come-first serve, show up early, possibly even before the rides are scheduled to start, if there is a specific bike (or bikes) you want to ride. I've seen single bikes get booked up completely within an hour if they're popular, and sometimes they were bikes I thought wouldn't be that popular.
When you show up, they'll check your license and you'll fill out some forms. These will be some basic personal info and also a release of liability for damage. They'll ask what bike you want, and you'll get signed up.
When it's your time to ride, one of the people running it will give a pre-ride talk. This is basically just some instruction of how you'll ride, where you'll ride, and some of the basic rules. Usually it's something along the lines of: Sit on your bikes, adjust your mirrors, get comfortable with the controls. You'll be taking this route. You'll be riding in a zipper/staggered formation. Don't slingshot, wheelie, stoppie, or go offroad. You're responsible for any tickets you may receive during this ride. There will be a lead rider and a chase rider. If you are going to get stopped at a light, please stop as required, and do not just gun it to get through. The lead pack will pull over to slow down if necessary, and the chase rider will make sure everyone stays on track. If there is something wrong with the bike, pull over and the chase rider will assist. Don't do anything stupid, and have a good time.
Once you finish the ride, you can usually go and sign up for another. Some dealers are pushier with the sales than others, but generally there is no sales pitch following the ride unless you want there to be. I've only been to one where a sales person came bugging me afterwards.