If you're new to SketchUp, use the following resources that I referred to when learning how to model:
SketchUp's official training [http://www.sketchup.com/learn]; free videos, downloadable step-by-step tutorials, and more, directly from the SketchUp team.
Google SketchUp 8 for Dummies, Wiley Publishing at http://www.aidanchopra.com/book-info, written by one of the SketchUp team members for SketchUp 8 in an easy-to-follow format. The vast majority of the book still applies to current SketchUp versions.
SketchUp School at http://www.go-2-school.com/, video training from experts, also available for free on YouTube at http://www.youtube.com/user/4sketchupgo2school.