Virginia Aronson, a nutritionist at the Harvard School of Public Health and author of "Thirty Days to Better Nutrition" (Doubleday, $10.95), offers these tips for improving a family's diet while reducing time spent on food preparation:

* Buy an inexpensive nutritional guide and use it to plan family meals several days, even weeks in advance. Learn to read the labels of products to check them for nutritional content.

* Prepare a shopping list a week in advance.

* While one family member does a week's shopping, another can prepare several dinner dishes and put them in the freezer for later cooking and use. It's as easy to prepare as much spaghetti sauce for six meals as it is for one, and other dishes, such as casseroles, are the same. These will be just as quick and easy to prepare as the highly processed frozen meals sold at the grocery, but they'll be a lot more nutritious.

* Draft the children into doing the kitchen cleanup after dinner each night and on weekends when future meals are being prepared.

* Instead of keeping potato chips, candy, or cookies in the house for snacks, keep a bowl of fresh fruit, low-fat cheeses, or crunchy vegetables such as carrots in the refrigerator. If the less-nutritious foods aren't available, your family will eat these instead.

* Use a microwave oven for dinner preparation, not just for heating leftovers. You can take something prepared in advance out of the freezer, pop it in the microwave, and have it on the table in less than 15 minutes. Inexpensive, attractive throw-away microwave cooking containers can be used to freeze foods, cook them and then serve them.

* When you do eat out, read the menu the same way you read the nutritional labels on the foods you buy in the store -- and make your selections on the basis of nutrition as well as taste.