While we've used SketchUp's Large Tool Set to fully build a model fit for 3D printing, we've only dipped our toes into what the full tool suite within SketchUp can do. I encourage you to look into the tutorials recorded by the SketchUp staff to continue refining your techniques. Ultimately the best way to learn is through practice. Keep trying to use the tools, get yourself into trouble, and figure out how to avoid trouble the next time.
Using arrays in your modeling is the most efficient way to duplicate objects (groups or components) in precise ways. Nearly every model you make will have some areas of duplicate parts. Arrays will help you achieve these duplications with little hassle.
Using components wisely in your model provides the same convenience of mobility as using groups, with the added opportunity to effect multiple updates and improvements simultaneously. A well constructed component will also help you leverage SketchUp's solid tools for 3D printing.
While SketchUp's Push/Pull Tool (Extrude) allows for extrusion along a straight line, the Follow-Me tool provides the same opportunities around corners, closed perimeters, and along curved paths.
Often overlooked, the Solid Tools within SketchUp are the unsung heroes when cleaning up multiple components and groups. For simplifying and cleaning up a model, they are powerful. For finalizing a model for 3D printing, they are almost essential.