Many runners, especially people who are new to running, make the "terrible too's" mistake. They get so excited and enthused about their running that they do too much mileage, too fast, too soon. They mistakenly think that "more is better" when it comes to running. As a result, they often start to develop common overuse running injuries, such as shin splints
, runner's knee
, or ITB syndrome
Be more conservative than you think you need to be with how often, how long, and how much you run, especially early on in your development. Increase your mileage gradually. Don't let your weekly mileage increase by more than 10%. If you're new to running or are coming off a long break, start with walking first, and then progress into a run/walk program.
Pay attention to aches and pains. If a pain gets worse as you continue runs, that's a warning sign that you should stop your run. Listen to your body for injury warning signs and know when you shouldn't run through pain.
Take at least one complete day off from exercise each and every week. Don't ignore rest days -- they're important to your recovery and injury prevention efforts. Your muscles build and repair themselves during your rest days. So if you run every day, you're not going to gain much strength and you're increasing your risk of injury.
Also see: 7 Smart Steps for Injury Prevention