Walk through the store and make a little mini map of where items are located. It may look like this
Produce- Fruits, veggies, nuts, dressings
Cereal- cereal, pop tarts, snack bars
Cookies- cake mix, cookies, fruit snacks...
This helps you to write out your grocery list in such a way that you don't have to hop from isle to isle haphazardly. And when time is of the essence this really helps me! Also I think that having such an effective list really helps to keep you on track with buying what you need, not just whatever you see.