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.