Yeah, injury is one of my issues. I have not been a consistent runner all my life and ramping up too quickly has lead me to a torn tendon (twice) which takes MONTHS to heal.
I've found success in spending time walking when I'm not running. I have a treadmill desk, but I also take part in long conference calls while walking around my neighborhood. Training your body to spend hours moving on a regular basis can help get you ready for increased running mileage.
