What are the most essential nutrients, which foods do you find them in, and what are some tips and tricks(about nutrition) to bear in mind while consuming food everyday?

This is really an impossible question to answer fully and/or accurately. There are many variables that change the specifics, many starting at the genetic level. Some genes work better with certain nutrients, but worse with others. Ethnicity and culture can play a role in determining which foods are available; when they can be eaten or must be avoided. Simple economics can determine what's possible. In general, nutrients -- and substances that support nutrition -- fall into broad categories and a healthy diet will include all of them to some extent. Among the categories: Carbohydrates Fats Proteins (including amino acids) Vitamins Minerals Water Each of these categories (water excepted) has a range of sub-categories that are important, each in its own way. The amounts of each vary in every foodstuff and the quantities needed vary by each individual. The sad fact is that at this point in human history, we really don't know what constitutes the healthiest possible diet. We can identify a minimum diet that provides for survival -- consume less of the various parts and you run into health issues -- but we cannot say what works best for everyone. Some people thrive on fully vegetarian diets; others thrive on diets that have almost no carbohydrates of any kind.