Make a list and don't put anything in the cart that is not on it.
Don't go down the cookie/snack/fatty aisle; you can't put it in the cart if you can't reach it (not being sarcastic - but realistic - it works wonders!!). Last, if temptation wins and you reach for the cookies, flip them over and read the fat grams, sugar content, and caloric count. If that doesn't work, read the nutritious facts and how much they do not help your health.