“Only people willing to work to the point of discomfort on a regular basis using effective means to produce that discomfort will actually look like they have been other-than-comfortable most of the time. You can thank the muscle magazines for these persistent misconceptions, along with the natural tendency of all normal humans to seek reasons to avoid hard physical exertion.” Mark Rippetoe
Eat meat and vegetables, nuts and seeds, some fruit, little starch and no sugar. Keep intake to levels that will support exercise but not body fat.
Practice and train major lifts: Deadlift, clean, squat, presses, C&J, and snatch. Similarly, master the basics of gymnastics: pull-ups, dips, rope climb, push-ups, sit-ups, presses to handstand, pirouettes, flips, splits, and holds. Bike, run, swim, row, etc, hard and fast.
Five or six days per week mix these elements in as many combinations and patterns as creativity will allow. Routine is the enemy. Keep workouts short and intense.
Regularly learn and play new sports.