I'd actually say that the most impactful first habit is regular exercise. Especially a few hours of strength training and a few hours of aerobic exercise per we

I'd actually say that the most impactful first habit is regular exercise. Especially a few hours of strength training and a few hours of aerobic exercise per week. You can have a mediocre diet and still see huge health benefits. The opposite is not true: a sedentary lifestyle will kill you and the last years will be miserable with little in the way of physical autonomy.