A good rule of thumb is to combine lots of different colors at each meal to ensure that you get a wide variety of phytonutrients (i.e. antioxidants, carotenoids, flavonoids, etc.), which help to prevent and fight cancer and other disease as well as providing protection from many other illnesses.
Furthermore, eating more vegetables will ensure that you meet your daily recommendation of 35 grams of fiber. Fiber is important for several reasons: it helps to improve cardiovascular health, improves intestinal motility and bowel function, helps you lose weight, stabilizes blood sugar, and gives you a sense of fullness. This is a very abbreviated list so just remember that fiber is critical to your health.
You will never have a fiber issue again if you simply eat your fruits and vegetables every day!