Contrary to popular notion of doing something in group, Do something Hard, Do something Lonely.
Practice something very individualistic and something that that most others will be unwilling to do. This will help you feel tough, help you concentrate, boost your ego and make you feel special. It will mentally prepare you for the business battles. Remember, it does get lonelier at the Top.
Something that is hard and lonely is studying for a graduate in film making, especially in winter, when everyone else is snoozing under their sheets. Or running slow over long distances at 4:00am in the morning (versus jogging with a million others at the fitness club in the evening).
Learn carpentry, write a book, read Tolstoy, but do it yourself. Do it alone and solo.
All the great and successful athletes and artists that you admire did have endless hours of toil when the world was sleeping. So do corporate Presidents.