The drawing area and drawing units are often the most mystifying aspects of AutoCAD, if only because they have few limits. Once you understand how to set up drawings for area and units, you can start to draw with more confidence.
Next, you'll want to brush up on your high-school geometry so you can understand the way AutoCAD determines the location of objects.
Since AutoCAD is all about drawing accurately, you'll want to become intimately familiar with the tools that help you maintain accuracy, such as osnaps and osnap tracking. This chapter covers all the osnap methods, but if you focus on just knowing how to get to them through the shortcut menus, you'll have all you need to make good use of osnaps.