1. Avoid foods that were unavailable before the advent of agriculture and animal husbandry (like dairy and grains). Instead consume mostly meat, fish, fruits, veggies, and nuts.
2. Exercise like early man. Perform short, intense bouts of whole-body exercises a few times a week: sprint, climb, swim, lift heavy things, wrestle, jump, and tumble. Most important, get dirty and have fun.
3. Focus on skills that have a real-world application. Instead of mindlessly working out, throw things, catch things, climb trees, jump from rock to rock, practice holding your breath, play with your dog, etc.
4. Stress your system. Skip a meal once a week or so. Try working out first thing in the morning without breakfast. Participate in something competitive, like a race or a game.