That's where an exchange list comes in handy. To meet your serving requirements from this food group, you would choose varied exchanges that constitute a serving. To offset boredom, the more varied your selections the better. A registered dietitian is the best source of an exchange list and dietary advice, or look for a good nutrition book at your favorite bookstore or library. Once you have exchange information, spend at least a couple of weeks referring to it for serving-size information.
Some product labels provide exchange information.
Checking product labels is a good way to obtain this information as well as calorie and fat content. As you become familiar with exchange classifications and serving sizes, you'll also want to become familiar with how many servings are appropriate for you. At a minimum, your individual requirements depend on body size, health and activity levels. Weight loss or gain requirements also come into play. The best person to take all these factors into account and come up with serving recommendations would be a registered dietitian.