You have to be committed to it or nothing will work.

Keep a food log. Write down EVERYTHING you eat and drink every day, with no exceptions. I've found that if I keep detailed track of what I'm eating, if I go to eat something unhealthy, it's not worth it for me to write it down, so I just don't eat it.

Like YB said, plan out all your meals. Keep your own cupboard, fill it full of healthy food and stay out of the other cupboards! You'll have to be very diligent in the beginning but as you learn how to eat right, it will become much easier.

What's your diet and exercise like right now?