Hello! I use sometimes the grease pencil, a quite unknown feature of blender, very useful for things like adding references, or annotations to our scene. On this tutorial, I'll show you how to use it for drawing on the 3D View, and even animate that drawings.
This tool is even more useful when you're working with a team, because it make it easy to mark things, show ideas and things like that on the scene for your coworkers, even they are on the distance :)
Hope you like it! See you!