Compare prices - comparing prices of goods is always a good idea. Sometimes coupons can help with something that is already a good price.
Cook your meals yourself - home prepared meals can be as cheap as $0.45 a person, or as expensive as $30 a person. It depends on what you buy. More expensive does not always mean better; however you can't usually eat out for less than $4 a person, and at that price it usually doesn't taste very good.
Budget - one of the best budgets I have found (and I hate budgets) is from Dave Ramsey. He writes down everywhere his money is going for the month, and he even gives himself a little "blow" category (the one you can use to spend money on yourself). Even when your "blow" category is $5, it's nice to know your not stuck to something so ridged.
Buy in bulk - this doesn't always mean cheaper, but it can. This is one of those compare things.
Use half the meat (it tastes just as good, just not as heavy) - this is great with most things however I suggest sometimes you use a filler like oatmeal or beans. This is especially important with hamburgers or sloppy joes. When making a taco or something skimp a little on the meat and you usually can't tell. I can never tell in my casseroles. Just don't tell your husband. ;)
Only eat until you feel comfortable - it is surprising how much you can save by eating less. It is also a nice diet tool. ;) I hate diets; however I find if I just eat until I am comfortable, or no longer hungry; I eat a whole lot less and I don't gain weight. I don't deprive myself of any food, I eat cookies and cake, but just half a piece.
Grow a garden - this isn't always easy for those that don't have any land (like living in apartments); however I have seen some pretty ingenious edible flower beds and potted plants. Check out this blog.