Firstly ask yourself if you really want to lose weight, as being honest with yourself is the first step to success.
Think about what your food or drink weaknesses are, if you don't think you have any ask someone close to you they will be able to tell you. Just for one week try and cut right back or cut out completely the worst offenders see what difference this makes to your weight. If you lose weight try thinking about why you need this food or drink in your diet at all.
Finally make a plan of action, think about how much you would like to lose and give yourself a timeline for when you would like achieve this by. Be realistic if it took ten years to gain you will probably need more than a month to lose it. Remember it's not simply what we eat but how much of it we eat so do check your portion sizes.