As you are creating your meal plan, write your grocery list at the same time. Be sure to check your pantry for items you may already have or often used items that you are low on. Try to include everything you need, so you only have to visit the grocery store once a week. One visit will help to eliminate the need to go to the store for "just one thing" which usually results in a few unplanned extras, including unhealthy impulse snacks.
One important aspect of making menu planning work for you is to stick to your list while in the store. This is easier said than done since grocery stores spend lots of time and thought on product placement to get you to spend more.Try to eat a small meal or snack before your grocery visit so that you won't be tempted by impulse items. It may also be helpful to organize your list by sections of the store so that you can get everything you need in that section, avoiding zigzagging back and forth trips through the store. If you don't have to go down a particular isle, skip it. It will save you time, keep you from browsing unnecessary items and keep you from succumbing to any of the grocer's marketing tricks in that aisle.
Reuse your weekly menu plans. After you have created a few weeks' worth of plans, you may find it helpful to keep them in a file where you can access a week at a time. This can be helpful when you simply don't have time to sit down and plan. Keep a grocery list with each menu as well, so that you can just take it and go.
Keep a running list of grocery items that you run out of. Either use a magnetic refridgerator list or keep a piece of paper when you can easily get to it. Everytime you use the last of something, write it down. This will help you stick to your list when you do your shopping and only make one grocery visit.
Be flexible with your menu. If you've had a really terrible day, and it's within your budget, getting take out or dinner once in a while won't ruin your healthy diet. The same goes for your list. If you see something you know you will use that is a great deal or if you forgot to add an important often used item, go ahead and get it.
If you need some help building a well-balanced diet, there is no longer the need to try to deciper the food pyramid. The USDA has its own free menu planner online called MyPyramid. It gives you a meal plan based on your calorie needs and takes into account dietary restrictions you may have.
If you need some help on meal planning, Menus4Moms.com is a site that offers menu planning services, but they also have a free e-course about menu planning.