D!!!!! Spend less than you have coming in! There's an old saying that earning 1 penny more in a year than your expenses is a recipe for happiness, earning 1 penny less, a recipe for misery.
credit is a very powerful tool, but should probably be used sparingly. In general, spend enough less that what you make to build up a cushion for emergencies, so you don't have to borrow for them, either. We call ours the "oops fund" and it's a life saver when something breaks and has to be replaced -- these things never happen at a time when extra money is floating around.
