The single best way to cut back on expenses is to use a price book. A price book is simply a way to keep track of prices so that you know a good price when you see one. The benefit of a price book is that you will pay the lowest prices on almost everything you buy on a regular basis, so you can substantially reduce your expenses on groceries and household items (and put that savings toward paying off debt or into an investment vehicle).
Here's how it works: A very basic price book lists an item and its lowest price per unit that you've been able to find. For example, you might list "size 3 diapers" at $0.25 and "size 4 diapers" at $0.29. The next time you're buying diapers, you'll know if the package of 48 size 3s that's on sale for $10.99 is a better deal than the package of 72 that's selling for $18.49. The cost per diaper in the package of 48 is $10.99/48 or 23 cents. The cost per diaper in the larger package is $18.50/72 or 26 cents. In this case, you would buy the smaller package and also write down the new low price.
You may find it helpful to keep track of other information, too. I usually write down the store that I found the lowest price at, the date, the size of the package, the total price in addition to the price per unit, and whether I used a coupon. This method works with just about anything you can think of: toilet paper, toothpaste, spaghetti sauce, meat, etc.
A price book can be maintained in a notebook or a computer file. If it's on computer, you may want to print it out until you are able to recognize a really good deal without having your price book on hand. Most cell phones have calculators now, so just pull that out to do a little math while you're at the store and decided which item is cheaper at a per unit cost. (But remember to buy the larger package only if you're going to use it, otherwise, you're not saving money.)