Round is a shape, right?
Seriously though, eat natural foods and walk. If you have a dog take him/her with you. Walk briskly for two miles, every other day.
Resistance train (lift weights) once each week. Alternate using a squats/chins or deadlifts/dips protocol. If your resistance session lasts more than 45 minutes, you aren't lifting heavy enough. A person can work long, or they can work hard, but they can't do both without added chemicals (bad stuff).
Exercise is a type of medication, and too much is just as detrimental as too little. Every person is different in their ability to recover from intense exercise. Don't be afraid to find the right regimen for you. If you can't add one-half pound to the bar at each workout, you need more rest between workouts. It really IS that simple.