Actually, it's pretty straight foward. Take a simple example, 1" = 1' scaling.
I'm going to assume you've never done this. So, with a page being displayed, draw a 6" square. Visio defaults to 1:1. Now, go to File > Page setup. Select the Drawing Scale tab. Choose Pre-defined scale. Keep Architectural. Hit the pop down list arrow, and choose 1" = 1' 0". You may have to scroll to find the entry. Select OK.
Now, your square will look smaller, but, it's still 6". That's the nice thing. Your drawing dimensions remain intact, they just fit on regular sized paper. If you have dimension shapes, they will still report correctly.
That's all there's to it. You can play with other scale factors, or define your own with Custom scale.
It's a lot better than trying to find a very expensive printer that will produce a 5' x 6' output!

Wapperdude