It's easy to over complicate healthy eating. We can start by going over proteins, fats, and carbs, or digging into micro-nutriants and their affect on a healthy metabolism, but I am going to start simple.
Eat real food.
Thats it! The magic pill, the kryptonite, the silver bullet, and the end all fix all for nutrition. Is it more complicated then that? Yes, but this simplification is enough to get results for almost everyone.
What is real food? Vegetables, meats, and fruits. Shopping at the store you should ask yourself, can I find this in nature? Chances are, if its in a box or a bag or both its not real food. This doesn't apply to everything, such as frozen vegetables, but its an easy rule to follow. The nutritional density of food it linked to its processing. The more processed it is, the less of the original nutritional value it retains. In an ideal world we could all have little farms and grown our own food, but that's not realistic for most people. Learning to navigate the local farmers market or grocery store is essential for finding the most nutritiously dense food. (continued below)
Eating healthy does not happen overnight. It will take time and many burnt or botched meals to hone your cooking skills. It is not easy to change a lifetime of habits, so be patient and be ready for delays. Check out the links above for more resources on eating healthy. Keep in mind, that while I recommend these resources, that does not mean I fully endorse everything stated in these resources.
The value of food should be judged on its nutritional density. Meat, veggies and fruits are the most nutritiously dense food options available. The micro/macro nutrients and everything inside and outside the food provides the chemicals necessary for our metabolism to work.
Your metabolism is every chemical reaction that occurs in your body to sustain life.
If you have a nutritiously deficient diet your metabolism will struggle to keep up. It will steal nutrients from one process to feed another, more vital, process. Keep your metabolism at maximum efficiency by eating the nutrients that will provide the resources it needs.