Get out and run.
Do not worry about the rest.
Make running a lifestyle. A daily habit, like brushing your teeth. If you run 300+ days a year, every year, for several years, good things will come your way. Start now. Doesn’t matter if you are 16 years old or 66.
If you want to be a decent runner you must get out and run; the rest is just noise.
Get the running in first— that is the foundation. Then: Eat mostly good stuff. Get enough sleep. Stretch if you want to— or don’t. Lift if you like lifting. Cross-train if it makes you happy. Wear minimalist shoes or big bulky ones, whichever you prefer. Listen to music when you run, or not. You can carry water with you on a long run, or you can go without. If you want to do a core routine, then do it— but first you must get out and run.
Run on trails, or streets, or on a treadmill, whatever works for you. Run slowly. Run quickly. Run up hills. Run in the rain. Run in the snow, the heat, the cold. Run into the wind. Run on the days that you do not feel like running. Run on the days that you can’t wait to get out and run. Run with friends. Run alone. Run races. Run in the country. Run in the city. Run in parks. Run when you feel happy. Run when you are depressed. Run when you have a ton of energy. Run when you are feeling like shit. Run when you feel good. Run in the morning. Run at night. Run before work. Run after work. Run."