Dividing your gym life into 3 segments: Nutrition, Training and supplements. Nutrition is probably 75%, Training 20% and supplements 5%.
Nutrition provides your body with the nutrients required to sustain, build and repair. The body needs constant supply especially during rest days when the body recuperates the most. Creating a varied diet with the correct Macro and Micro Nutrients will enable you to be the best you can be, prepared for intense workouts and great gains.
Protein, Carbohydrates and Fats are the main macro nutrients. These are the main focus when starting out or the first thing that will get looked at to see if there is lack of or too much.
Micro nutrients is the finer detail, including vitamins, minerals, sodium and iron. These are usually fine tuned when the Macro Nutrients are sufficently in place.