Keep fit! Exercise lots, drink water, push yourself! Do something physically challenging to you, such as Karate, CrossFit, Parkour, Fencing, any kind of sport or just running and daily workouts.
Photos: http://midnight.hushedcasket.com/wp-content/uploads/2008/04/crossfit-forging-small.jpg; http://www.nwaparkour.net/parkour-logo.jpg; http://www.mcleancenter.org/elements/image/Fencing%20Match.jpg