Remember when Oprah lost 67 pounds and wheeled a wagon full of fat on to stage? It was definitely bizarre, but it served its purpose and going cash only does the same thing for your finances. While not as explicit as Oprah's wagon moment, I think deciding to only spend cash is really eye opening. You get a real visual of how much money you're going through and where you're spending it when you're shelling out actual cash.
If you're someone who's always wondering where your money went at the end of each month, a good idea would be to completely ditch plastic for awhile. That means using absolutely no credit cards, and using debit cards only to pay your online bills. Even if you already primarily use your debit card and save your credit card for real emergencies, you're still not having to hand over cash every time you make a purchase. You're more likely to consider what you're buying if you have to keep running to the ATM.