When using the Trim or Extend commands, the first prompt is to “select cutting edges” (or “boundary edges” for Extend). Hitting ENTER turns everything in the drawing into a cutting/boundary edge, so you don’t have to do it manually.
I've been sending these tips out to my office once a week for about three years now, and decided to start the blog as a way to put them all in one place. Who knows, maybe they'll help somebody else out there too!
Some of the tips are pretty basic, but hey, we all had to start somewhere.
Most of the tips apply to AutoCAD 2004 & up -- I'll try to note if it's only available in later versions, but no promises. And ALL the tips apply to AutoCAD LT.
As always, if you have a tip you'd like to see featured, send it on in!