Eat nutrient dense foods.
What I mean by this is eat foods that have low calories and lots of nutrients. If two people have diets that contain 2000 calories, one person might obtain those calories from sugar in their two to three coffees per day, doughnuts, bagels, cookies, etc... There would be lots of calories but little nutrition. Another person might have the same calories in a given day but obtain them from fresh salads, beans, steamed vegetables, limited animal protein, nuts, etc.... Obviously, all calories are not equal and you will get more bang for the buck if you are less like the first person and more like the second.

Eat unadulterated and unrefined foods.
The more we mess with food, the less nutritious it becomes. Anything that is packaged with a catchy decorative logo or design is usually an inferior food choice. Cooking also destroys some of the good things in foods. I am not saying that we should only eat raw foods but at least some of our diet should include raw fruits and vegetables. Raw foods contain enzymes that assist in our digestive process.

Shorter shelf life = Better nutritional value.
If it cannot spoil, then there is nothing in it worth eating. For example, refined flour, used to produce most breads and baked goods, lacks the fiber and nutrients contained in unrefined, whole grains. The nutrients in whole grains are perishable. Without them, products have a much longer shelf life. This is why a package of white flour can sit on a grocery shelf for an indefinite period of time without spoiling.

Eat colorful foods.
Eating foods of different color is pleasing both to your eyes and your health. Research shows that different antioxidants are found in yellow foods, red foods, green foods, etc... The variety of nutrients helps strengthen our immune system in many ways.

Eat some fat.
We need fat in our diets. Some estimates say that up to thirty percent of our calories should be from fat. Fat is needed for the production of all hormones. Some fat in the diet helps us feel satiated when we eat. This allows us to feel full and stop eating. Without this feeling we may overeat and consume too many calories.

Keep in mind that there are different kinds of fat. If all your fat comes from animal products and shellfish, you are eating too much unhealthy saturated fats. You may want to eat less of those foods and more avocados, walnuts, olive oil and fresh fish that contain healthy unsaturated fats. Research is showing that saturated fat has more of a pro-inflammatory effect in the body whereas unsaturated fat has an anti-inflammatory effect. The medical term for inflammation is the suffix "-itis." This is Latin for inflammation of whatever the prefix is. If the diagnosis is colitis, then it means inflammation of the colon. If the diagnosis is sinusitis, that means inflammation of the sinuses. As you can see, there is a lot of inflammation contributing to ill health. If you are a sufferer of an "-itis" then taking steps to reduce the inflammatory process is a good thing.

It is also important to avoid false fats such as hydrogenated fats. These are man-made, adulterated fats that increase the cholesterol production within the body.

Eat Fiber.
Most people do not eat enough fiber. One of the first books to address its importance was The Save Your Life Diet by David Reuben MD in 1975. In his book, Dr. Reuben documents how the high fiber diets of primitive societies can be a useful deterrent for many illness of modern society. James Anderson, author of Diabetes, a Practical Guide to Healthy Living, took 20 non-obese men who were insulin dependent (that is, injected themselves with insulin) and gave them 65 grams of fiber per day. After 16 days, the average cholesterol went down from 206 to 147. The insulin needed was reduced from an average of 31 units to 16 units. Eleven out of the twenty participants discontinued insulin injections completely. One hundred percent of the participants showed clinical benefits and the benefits continued at home when following the same program.

Be aware of your special needs.

Avoid foods that you are sensitive to.
Some people know from experience which foods they need to avoid. If you have a lot of sensitivities, then chances are you need to do some cleansing work. In addition to gluten, the foods that people are most often sensitive to are dairy, sugar, corn, eggs and caffeine. An excessive amount of any of these foods in a diet will cause different symptoms. Children with chronic ear infections usually need to remove one or more of the above foods from their diet. The same would be true of adults with irritable bowel disease.
Be aware of food combining principles.
This is important if you tend to have a lot of bloating or gas after eating. According to food combining principles, it is better to eat certain combinations of food at the same time. Look at the figure below. The rule is: Where there is a line you can combine.