I found this useful bit of advice during a search for something else:
> … you can create a template that will load when you open SU that deals with the scale issue you mentioned. Open a new drawing. Draw a square in the center that’s about average size for the things you draw. Zoom into give an acceptable view. While you’re at it set display settings. I like to start in perspective view, Hidden line, profile lines turned off, shadows off, white background.
> Next delete the square so you have a blank drawing space. Save As My Template or whatever you want to call it. Save it in the Templates folder under SketchUp. Find the Preferences dialog under Window in SU. Set the Drawing Template to whatever you just named that drawing you saved. That’s all there is to that one.
My thanks to Dave Richards of Rochester, Minnesota who contributed that to a discussion on the Sawmilll Creek forums — Sawmill Creek is an online community for woodworkers.