Quick Clue - Select Similar

This is one of my favorite tools inside AutoCAD, I use it all the time in Civil 3D and if you are not using it on a daily basis then you should be!

The command does it exactly what it says, Selects Similar objects. So if you are in a drawing with control points or contour labels and you want to change the properties of those labels quickly just select one and right-click, and the Select Similar command is at the bottom of the menu.