Mind Your Layers
Sometimes they are called layers. Other times they are called levels. Either way, they are very helpful in CAD, 3D modeling and pretty much any other design or creation software.
From the Autodesk support page for AutoCAD:
With layers, you can
* Associate objects by their function or location
* Display or hide all related objects in a single operation
* Enforce linetype, color, and other property standards for each layer
Important: Resist the temptation to create everything on one layer. Layers are the most important organizing feature available in AutoCAD drawings.
When I first start a project I often have the temptation to jump right in and make something happen. The sloppier I start out, however, the more of a mess my project will be later on. Layers are not only important, but you need to start using them from the very beginning of your project.
So next time you start a project, remember this little PSA and mind your layers.