Object Snaps (OSNAP) are among the most fundamental AutoCAD topics I know. Without them, drawing two intersecting lines can be described as arbitrary at best. A lesser known OSNAP function is this thing called Object Snap Tracking. Simply put, Object Snap Tracking can reduce if not eliminate the number of construction lines you draw, just to erase moments later.
To use Object Snap Tracking you must first have both your Object Snaps (OSNAP), and your Object Tracking (OTRACK) turned on.