AND IT LOOKS AWESOME!!! I followed the advice in this article:
I've given myself a trim from time to time before, but this method is to give yourself layers. I did not cut mine as short as the lady in the article, and I also didn't do the vertical cuts at the end for as long as she said she did (five minutes would have left me with no hair at all!). It came out gorgeous- much better than any salon I've ever been to. Very pretty, natural layers that aren't chunky or choppy at all. Mine don't look as '70's as hers do, either.
I highly recommend trying it. I did it today because I had the time to go immediately to the hair salon if I really messed it up, so that helped with courage. I also did it twice- once without cutting much length at all, just to be cautious, and then a more dramatic change after I realized the method actually worked.
I sort of can't wait to tell people I did it myself!!