In terms of money, we are often our own worst enemy. We promise ourselves we're not going to spend, then we somehow end up with two new shirts. We decide to really buckle down and start saving for retirement, only to wind up with a new pair of shoes in our closet.

Why does this kind of self-sabotage happen, no matter how hard we try to prevent it? As it turns out, at least part of the blame can be pointed at your brain.

That's right, your brain. It no doubt spends a lot of time working for you -- it's involved in every little thing that you do, from breathing to buying those shoes -- but it can also work against you if you let it.

"Your brain will give you a lot of emotional signals, and some of them are not very useful -- in fact, they can be quite misleading," says Dr. George Loewenstein, a professor of economics and psychology at Carnegie Mellon University.

Knowing how to interpret the signals and perhaps ignore the ones that may lead to trouble is key to getting your financial life in order.

-- Use your willpower wisely. You probably think of willpower as a renewable resource, but surprisingly, it may not be. "Psychologists have found that there's this thing called eco-depletion, where you have that "oomph" for controlling yourself, but it's like a muscle -- you can wear it out and run out of willpower," says Sam Wang, an associate professor at Princeton University and co-author of "Welcome to Your Brain." What does that mean, exactly? It means that if you're trying to stop shopping or smoking, you shouldn't try to do other acts that require willpower at the same time. In other words, you'll have the most success if you prioritize your efforts: Stop smoking, curb your shopping habit, then work on that diet. The order, of course, is up to you.

-- Make your saving automatic. If you make automatic contributions to your 401(k) or other savings accounts, the money is out of your hands, out of your wallet, and therefore, you're less likely to spend before you can save. But there's another reason as well: Your brain doesn't do well with planning for the future. It's programmed to want things now, not later. We're more likely to agree to put a portion of a future raise into savings rather than a portion of our current salary, says Wang. "You can basically trick people's brains into doing the right thing by setting up situations where they don't quite feel the bite of what they're being asked to do." Put all of your savings contributions on autopilot and before long, you won't even notice the missing cash.

-- Think it through. "Your brain doesn't give you very reliable signals about when you should spend and when you should save, and the implication of that is that you really need to think it out," explains Loewenstein. This, in a nutshell, is why impulse buys are a no-no. How many times have you purchased something, only to regret it later? Sure, you can return it, but that's energy -- and often money, in the form of shipping or gas -- wasted. Next time, instead of impulse buying, sleep on it. If you're still thinking about it the next day or even the day after that, and you can afford the purchase, then go back and buy it.

-- Focus. Spend some time really thinking about what gives you pleasure. There is a good bit of research showing that we tend to get more pleasure from experiences than from possessions. That vacation with your family gives you memories that you can reminisce about time and time again. That new watch you don't really need won't give you quite the same effect. That doesn't mean you have to rule out buying things. What it does mean, though, is that when money is tight, as it is now, you need to put more thought into not only whether you spend, but how you spend as well.

-- Watch out for the "peanuts effect." Essentially, says Loewenstein, if the expenditure is really small, it feels like we're not spending any money at all. That's why you have no problem buying a cup of coffee or lottery tickets or a pack of gum. In your brain, they don't register as purchases. And while it's true that one pack of gum won't blow your budget, a pack a day certainly could. This thinking, by the way, can also sabotage your savings in another way. Your brain thinks a dollar doesn't add anything to your efforts, but when combined with another dollar tomorrow, and another the next day, the cash can really start to add up.

With reporting by Arielle McGowen