How to Draw Using a Plane as Reference

Who has never struggled trying to make a rectangle perpendicular to the ground in SketchUp? A good tip, not very well known, is to use an already-drawn face as a reference to make a drawing coplanar to that face. To do this, just hold down shift over a face, while using the drawing tool you want (rectangle, line, or arc), and move the mouse to where you want to start drawing. Without releasing shift, draw normally, and that's it—you have a drawing coplanar to the reference face.