To keep your diet healthy, you should try to consume many fruits and vegetables each day. The USDA recommended daily allowance of fruits and veggies combined is 9-13 servings a day. That sounds like a lot, but it's really not difficult to fit them in. Have a glass of real orange juice with your breakfast or put tomato pasta sauce on your spaghetti.
Choose whole grain over white breads. White breads are made from flour that has been highly processed and has lost much of its original nutritional value. Instead, pick whole grain breads. Not only are they better for your health, they taste better and are more filling, meaning that you eat less.
When you "study up" on nutrition, be sure to read about more than one approach. There is more than one school of thought, and fashions come and go--even in this supposed "science." In making a decision on which one to follow, the crucial test is what actually works for you. You may have to put more than one theory to the test before finding the one right for you.