Basics first: The brain is an organ. Physical health and brain health and mental health are deeply interconnected. Find a physical activity that you can do several times a week with minimal motivation. Bonus points if you get friends into the same activity, or the activity is something like a martial arts gym. Accountability to others is an incredibly powerful motivation. Use it for both long term habits (daily fitness routine), and one time large goals (I'll lose 50 lbs this year or I own my friend $200).

Optional but valuable: learn how to cook [healthy] food that tastes good. This plays into fitness, and also can become a hobby. At a minimum learn 1-2 dishes suitable for bringing to a party.

This last one took me the longest: Find out how to truly relax. This is where it comes full circle, and you learn to use your thoughts to control the body. The Reveri app hypnosis routines were helpful to me along this journey.