For some people, shopping is a form of therapy. Others get obsessed with big ticket gadgets and always feel the need to get the latest and greatest toy. It seems innocent, but this can be a real problem and prevent you from using that money in a much better way. To keep yourself from making such impulse buys, you must train yourself to change the process you go through when thinking about a purchase.
The first step is honestly asking yourself whether it is a need or a want. If it is a want, you should lean towards not making the purchase unless you can honestly justify its intangible value to you.
Next, you have to put yourself on probation. Every unnecessary purchase should be buffered with a mandatory waiting period you give yourself to think about before you buy. Try 2 to 3 weeks to start out with, especially with big ticket items like electronics or high end designer fashion products. If you have difficulty sticking to the waiting period, enforce it on smaller and smaller items like t-shirts, for instance, until you have a handle on your compulsion.
With practice doing this, you will have better control over yourself and will save a load of money in the long run. It is not to say you should never make a purchase for personal reasons, but it is always best to be in control and understand what is going on. That way you see things for what they are and can begin using money in better and better ways.