Combine interesting and complementary flavors, colors, and textures. Consider how flavors will work together; usually, one highly seasoned food is enough and can be rounded out by milder accompaniments (chili served with cornbread, for example). Think about how the colors and shapes of foods work together (fish, mashed potatoes, and parsnips seem dull in comparison to fish, a crisp green salad, and a wild rice pilaf mix). Think about temperature and texture too -- serving foods that are soft and crisp or cold and hot alongside each other will make meals more lively and varied.
Use the Food Guide Pyramid and the ABCs of good nutrition to help you plan how to eat healthfully.
One starchy dish (potatoes, rice, pasta, beans, or corn) is plenty with most meals. Bread can be served in addition to the one starchy dish.
Balance the courses: Alternate rich, highly flavored foods with simple, fresh items. For example, if you serve a rich, cheesy lasagna, dessert should be light and refreshing -- perhaps a lemon sorbet with sugar cookies. Also avoid repeating flavors; even when two recipes aren't served at the same time, consider how each dish will add character to the meal.