One: Always start gently, with a warm up such as a 10 minute brisk walk and some gentle stretches.
Two: Pace yourself. It is better to do small, regular amounts of exercise than a large amount all in one go.
Three: If joining an exercise class, ensure that your instructor is qualified and always tell them if you have any areas of concern. You should have plenty of space to move in and the exercises should be fully explained.
Four: Listen to your body. Never exercise to the point of exhaustion - if it's starting to hurt don't push yourself further. If you have started a new sport such as swimming, start off by swimming just a few lengths and build up your stamina gradually.
Five: Always make sure you have a bottle of water to drink during and after exercise to prevent dehydration.