The Marine Corps primary method of improving the cardiovascular fitness of its marines is running. Typically, a marine runs at least 3 miles every other day. Before you start running, make sure that you are wearing running shoes that are appropriate for you; they should be neither worn nor ill fitting. During the run, when breathing, inhale through your nose and exhale through your mouth. Additionally, your arms should swing naturally at your sides. Runners World and About.com offer excellent advice for runners of all ability levels.