First, make sure someone has put it on some sort of events calender...like the one last weekend in Washington DC, on the Friday before the HUGE anti-war march. Yes, critical mass does not need to be only on the last Friday of every month.
Then get together with a bunch of friends and load all your bikes in a pickup truck or minivan.
This is a great way to get more people to go out of town.
Then find some cheap accomodations near the action. Hotels can be a cheap way to go, especially if you split up the rooms and some places are even bike friendly.
Then get to the rally spot for the start of the ride.
Sometimes the cops will leave you alone so its best to ride on into the night with your new found friends.
Thanks to Jamie for the pictures.