A specific nutrient that some of us need to focus on is iron. Foods high in iron are pumpkin, sunflower, and sesame seeds, some dried fruits such as dried apricots and raisins (which are also good for iodine), dark leafy greens, beets, and beans and legumes such as lentils. If you are prone to iron deficiency eat these foods at least once a week. If you feel tired, run down and sluggish, eat some iron-rich foods and see if you feel better.
Many people also need to supplement their vitamin B12 which helps the body to absorb iron. Most people over the age of 50 are deficient in B12 including people who eat animal products. The best way to get more B12 is to gently wash root vegetables from a quality source instead of scrubbing or (gasp) peeling them. Nutritional yeast is also high in B12.