Healthy eating involves three basic things:
First, getting your body all the nutrients it needs for optimal functioning. There are a lot of debates over the ideal diet, from high-carb to low-fat to vegetarian, vegan, macrobiotic, and so on. I personally believe that people respond differently to various diets, and therefore should find that which suits their bodies best. But the bottom line is that, whatever your diet, you need to get enough of all the nutrients needed for good health.
Second, getting those nutrients absorbed into the body and used. This means that the FORM of those nutrients needs to be absorbable, and that your cells must be communicating properly throughout the body for proper usage.
Finally, avoiding those foods that reduce your physical health. For instance, anything that's manmade (i.e., artificial colors and flavors) is by definition foreign to the natural, physical body. Our bodies adapt in myriad ways to the bizarre things we put inside, but these adaptations are short-term solutions to avoid more dire results.
Of course none of us eats a perfectly healthy diet, but when we talk about diet, we should understand these three points as the basis for the ideal. So how do we strive for that ideal? The following articles tackle it one point at a time.
Please also see the related article on Recommended Supplements. (How to choose, and what I use.)