Especially for beginners, it's important to fit in a run at least three times a week — even if you have to do a run-walk combination at first, Lyuda Bouzinova, an ACE-certified personal trainer and co-founder of Mission Lean, told POPSUGAR. Once you've gained some experience, you can technically run every day, but Lyuda recommends varying the intensity — keep your most challenging runs to two to three days a week, and alternate them with easy, slower-paced runs. In order to prevent injury and maintain endurance, you should strength train during the week, too.