A common pitfall with many new, as well as seasoned AutoCAD users, is to not read the entire command line to use it's vast array of options.  After mastering a certain pattern of commands and responses users tend to treat the command line as something that's only needed every once in a while.  It's the same principal as when you master typing, the need to look at the keys is not there any longer.  This tip is very simple.  Start a session of AutoCAD and force yourself to read the ENTIRE command line.  Yes, every line, not just the first line of a command.  Doing this for several sessions or at least once a session should enlighten most users to a few hidden treasures that were overlooked before.  Use the F2 key to toggle the command line to a larger version anytime in your editing session.

 Here's a classic command line option for dimensioning right under your cursor:

Issue the Linear Dimension command.

The command prompt reads: Specify first extension line origin or <select object>:

Issue a return to accept the <select object> option.

The command prompt now reads: Select object to dimension:

Yes, you can just issue a return and simply pick an object and then place the dimension instead of picking two separate points as the origination points .

Remember, sometimes we look but we don't see.