Once the basics above feel familiar, a little deeper reading helps the pieces click together. Two ideas are worth understanding well because everything else sits on top of them: energy balance over time, and protein distribution across the day. When those two make intuitive sense, most nutrition advice becomes easy to judge.
Sleep and recovery are also worth a read. Short or poor sleep tends to raise appetite and make training feel harder, so they quietly affect both fat loss and muscle gain. Understanding why recovery matters often does more for results than any new food rule.
Most useful of all is learning to tell evidence from marketing. Be a little skeptical of products that promise fast results, secret tricks, or anything that sounds too good to be true. Look for guidance from public health authorities, registered dietitians and researchers rather than supplement sellers. Knowing how to read a claim is the skill that protects you for life.
A closing note: this page is general education, not medical or personalized dietary advice. If you have a health condition, are pregnant, are under 18, or have a history of disordered eating, talk to a doctor or a registered dietitian before making big changes.