* Stretch all of your major muscle groups - gently - before and after any workout.
* Use all safety equipment such as cleats, mouth guards, knee pads, etc., that are associated with your sport or activity.
* Learn new activities with someone knowledgeable (a coach, health club instructor, or gym teacher) before trying anything on your own.
* Know your limits. If you are new to exercise, take it very easy your first few times or during your first few attempts at a new activity. You may feel fine at the time, but chances are, new activities will make you somewhat sore the next day even if you don't overdo it.
* Avoid over-training. Too much exercise can be as bad as too little. You can significantly increase your risk of injury and burnout if you exercise too long or too often. Be sure to take at least a day off each week to let your body recover.
* Drink plenty of water before, during, and after your workouts. Drink even more on hot days when you exercise outside. Even when it's cold, you still sweat and need lots of water to stay hydrated.
* Listen to your body. Pain is a signal that something is wrong, and you should respond by resting. Don't try to "work through the pain" or you risk more serious injuries that could bench you for a long time.