Carnegie Mellon University
Healthful eating requires common sense, some pre-planning, and basic, sound nutrition knowledge. By following the guidelines listed below you will be able to meet your nutritional needs and maintain a healthy body weight.
In fact, eat 3 - 6 times per day. Your metabolism will be more efficient and burn calories more effectively if you keep the "fires burning", so to speak, by eating every 3 - 5 hours. Eating small frequent meals will also help keep your blood sugar and energy levels steady. Visit ChooseMyPlate.gov to obtain a food group and portion size eating guide tailored just for you. 
Resist the temptation to eat in front of the computer, while using your smart phone, or during reading, etc. You will get more satisfaction and pleasure out of your food if you pay attention to what you are eating! You may also be able to stop at the first sign of fullness and avoid overeating.

Eating protein, complex carbohydrates and fruits and vegetables each day will help you meet your vitamin and mineral needs. Don't rely on supplements. Eat real food and use a multivitamin and mineral supplement only as added insurance. 

Carbohydrates supply energy to the body in the form of glucose, which is the only energy source for red blood cells (carriers of oxygen for energy) and is the preferred energy source for your brain.  Fruits, vegetables, whole grains and fat-free or low-fat milk products are all important carbohydrate sources. Choose complex carbohydrates, like cooked, beans, peas, and lentils; whole grains and cereals like rice, bran, oats, couscous and barley; vegetables, including potatoes; and fruits.

Select low-fat protein foods like lean red meats; chicken and turkey breast without the skin that is baked, grilled or broiled; low or fat-free dairy products; eggs; fish and shellfish; cooked dried beans, peas and lentils; and tofu or other soy products. Including a protein source with meals or snacks will help feel satisfied and focused.

Fats in the form of liquid oils are necessary for a healthful diet and low intakes increase the risk of inadequate intakes of vitamin E and essential fatty acids. Enjoy sources of polyunsaturated and monounsaturated fatty acids such as fish, nuts, and vegetable oils.  Limit your intake of saturated fat from fried foods, and fats that are solid at room temperature like animal skins, hydrogenated oils, and whole milk products.

Eating 2 ½ - 4 ½ cups of fruits and vegetables daily along with other complex whole grain carbohydrates will give you the 20 - 30 grams of dietary fiber you need each day. It will also help you meet your vitamin and mineral needs. Any and all fruits and vegetables are encouraged; in particular choose dark green and orange colored fruits and veggies several times a week.
Include a full glass of water with all your meals and take a water break a few times a day. If you do not like to drink water, try adding a lemon wedge, or choose sugar free/calorie free flavored waters instead.

Sugar
Foods high in sugar are often high in fat and calories and devoid of vitamins and minerals, thus the name "empty calories". Eating an excess of sweet foods can also contribute to tooth decay. The major source of added sugar in our diet comes regular soda, energy drinks, specialty coffee drinks, sports drinks and other fruit based beverages. Think your drink! There are as many as 17 teaspoons of sugar in one 20 ounce regular soda.

Salt
Limit your sodium intake to 2400 mg/day. That's the equivalent of approximately 1 teaspoon of salt. Remember to count the sodium that's already in the foods you are eating, not just what you add at the table. Learn to look at the Nutrition Facts Label. Choose foods that are low in sodium, less that 140 mg or 5 % daily value (%DV) per serving.

Caffeine
Caffeine gives you immediate energy, but you will pay for it with a rebound drop-off in energy later on. Remember we get energy only from the foods we eat.  Caffeine in the late afternoon and evening can interfere with a good night’s sleep.

Alcohol
If you drink, drink in moderation. Moderation means no more than 5 servings of alcohol spread out over a week (not all at once). A serving is 1.5 ounces of pure alcohol, one 12 ounce beer, or one 5 ounce glass of wine. Excessive drinking can lead not only to health problems, but also to excessive weight gain.