Choose whole foods instead of processed. Swap your frozen pizza and instant ramen with whole foods like fresh fruits, vegetables, and whole grains. They are packed with essential nutrients like protein, fiber, healthy fats, vitamins and minerals as opposed to processed foods which contain empty calories. “Commit to adding veggies to your lunch and dinner and fruit to your snack,” suggests DiCarlo.
Reduced nutritional density in many foods, combined with the use of refined "foods" like sugar, white flour and refined oils, places a greater priority on eating the most nutritious foods. Farm produce grown organically generally has higher levels of essential nutrients such as trace minerals because the soil contains higher levels of trace minerals and the produce grows slower and thus has more time to absorb nutrients from the soil. Examples of nutrient dense foods are sardines, wild salmon, shellfish, eggs, liver, kale, collards and spinach, sea plants (seaweed), garlic, blueberries, and dark chocolate. 
Fresh, Frozen, or Canned Fruits ― don’t think just apples or bananas. All fresh, frozen, or canned fruits are great choices. Be sure to try some “exotic” fruits, too. How about a mango? Or a juicy pineapple or kiwi fruit! When your favorite fresh fruits aren’t in season, try a frozen, canned, or dried variety of a fresh fruit you enjoy. One caution about canned fruits is that they may contain added sugars or syrups. Be sure and choose canned varieties of fruit packed in water or in their own juice.
Count nutrients, not calories. If you want to improve the quality of your diet, focus on the nutrients in your food instead of calories. “Our energy intake can only depend on our ability to extract that energy from food,” writes blogger and nutritionist Rhiannon Mack. “All calories are not created equal – it is the quality of the calorie that has the most impact on health, not necessarily the quantity,” she explains in a post that appeared in Move Nourish Believe.
Grains, vegetables and fruits are essential to getting the vitamins, minerals, complex carbohydrates (starch and dietary fiber) and other nutrients you need to sustain good health. Some of these nutrients may even reduce your risk of certain kinds of cancer. But experts say we rarely eat enough of these foods. To make matters worse, we also eat too much of unhealthy types of food, including fat (and cholesterol), sugar and salt.
A well-known example is vitamin C, which can effectively fight viral infections, prevent or reverse disease caused by bacteria, and help the body detoxify organic and inorganic toxins.  Vitamin C also reduces the risk for cancer, strengthens connective tissues (collagen), and counteracts stress by increasing the adrenal´s production of cortisol. The dose required is set according to the body's need. Nobel Price Laureate Linus Pauling suggested that an optimal daily intake of vitamin C could vary from at least 250 mg up to 20 grams per day.  Because unabsorbed vitamin C attracts water into the gut, some people may experience loose stools, gas and/or diarrhea by ingesting only 1-2 grams at a time, while others with a higher level of stress may tolerate 5-6 grams or more. The dose that causes loose stools is called the "bowel tolerance" for vitamin C.  To avoid the laxative effect of high doses, it is best to take vitamin C throughout the day in smaller divided doses.
Talk to your doctor before you begin taking a dietary supplement. They can tell you about the benefits and risks of each supplement. Make sure they know about anything you already take. This includes all medicines, prescription and over-the-counter. Some of these can interact with supplements. Read the ingredient list to make sure you know what else is in them. Do not take more than the recommended dosage on the label, unless your doctor approves it. Just because a supplement is advertised as “natural” doesn’t mean it’s safe.
In 2015, the Australian Government's Department of Health published the results of a review of herbal supplements to determine if any were suitable for coverage by health insurance. Establishing guidelines to assess safety and efficacy of botanical supplement products, the European Medicines Agency provided criteria for evaluating and grading the quality of clinical research in preparing monographs about herbal supplements. In the United States, the National Center for Complementary and Integrative Health of the National Institutes of Health provides fact sheets evaluating the safety, potential effectiveness and side effects of many botanical products.