In A Woman After God's Own Heart, Elizabeth George declares that a simple way to save some money is to go on a spending fast for a month. Determine not to buy anything that is not absolutely necessary.
Distinguishing between a want and a need can sometimes be a bit tricky, however. I can keep myself from going to Hobby Lobby for a month, and from the mall, and from online shopping. Where it gets harder for me is at the grocery store.