6. Don’t be afraid to change the camera type often. While the Perspective View can be used most of the time, it’s often useful to see plan or elevation views of the model. Switch to Parallel Projection view, then choose one of the Standard Views from the menu, or click the corresponding view icon (Windows – with the ‘Views’ toolbar open) or press Cmd-1 to Cmd-6 (Mac) to switch between orthogonal views quickly.
Don’t be afraid to change the shading view often either. So switch away from ‘Shaded Textured’ to X-Ray or wireframe to see if there’s any pesky stray geometry inside your model. Use the Hidden Geometry option to reveal edges incorporated into curved faces (with this selected, individual facets of a curved face become selectable).
Note that you can change camera or shading type during a tool operation – handy if you’re zoning in on an area of complex geometry while drawing.
This leads me to the last and most important tip about the camera. Remember the early 3D video games where the camera would suddenly and disturbingly clip your character or a piece of scenery and you’d see ‘inside’ the model? Well don’t be afraid to do that on purpose in Sketchup. If you zoom in on a part enough, the camera will clip the geometry and you’ll be looking at the ‘inside’ of the model – the part normally occupied by whatever material the object will be printed from. You can use this ‘feature’ to your advantage and seek out stray or unnecessary geometry that might affect your upload success. This camera clipping only works when the ‘Perspective View’ is selected. If you get lost, use Ctrl-Shift-E (Windows) or Cmd-[ (Mac) to show the whole model.
It was suggested to me that the Section Plane tool does this too (and in a lot of ways, is easier to use!), but I guess I just prefer ‘walking’ through the model. Try both techniques and see what you prefer.