When you've had the same long cut for years it's naturally hard to imagine chopping off most of your hair. Instead, start by cutting a few inches. If you like that length, next time go a few inches more. Another tip we got from the book, 'Confessions of a Beauty Editor,' by Allure's Linda Wells, is to take a picture of yourself in front of a dark background then take a Sharpie and 'cut off' your hair to see how you'd look shorter. We suggest starting longer then gradually going up so you don't waste your picture.
Wells also suggest wearing hair back in a ponytail to see if you'd be comfortable revealing your face in a shorter look. (Though my experience is women with long hair CONSTANTLY wear ponytails out of lazy habit, and going short actually offers them a way to finally frame their faces nicely).

