Don't go grocery shopping when you're hungry.
Make a list and STICK to the list.
Try this exercise, stay to the outside aisles and see how much of your list you can fill. Most of the junk stuff is on the inside aisles.
Don't be fooled by the advertisement of low-cal, natural, lite. Read the labels and you'll find out what is in that package of food you're about to buy and consume.
Buy the ingredients and make the item instead of buying it pre-packaged (i.e. Soup).
It takes time, but after awhile you re-educate yourself. I shop almost exclusively on the outside aisles where the produce, meat and dairy is. I don't even go down the snack/candy aisle any more. You see it, you want it, you buy it, you eat it. Don't give in!