Here -- http://www.crydev.net/viewtopic.php?p=819231#p819231 -- is a post for bringing SketchUP models into the new crysis (game) engine. Even if you're not interested in the crysis game engine (although it has really cool potential for realistic walkthroughs) or even rendering engines in general it has some excellent advice about proper modeling technique in SketchUP. It's pretty well written and includes a bunch of clear images illustrating each concept.
The main things I would take away from it are:
How and why to pay attention to which direction faces are facing
why and when to use groups
how to apply textures and basic manipulation of these
Just to be clear, 3. General advices on modeling is the section I thought would be helpful, although the rest of the topic would be interesting/useful if you have any desire to learn how to prepare a model for most any rendering program.