when u change your running form too soon u get hurt easily.
i think mid-foot running/ barefoot training /chi running can help in preventing some kinds of injury. But it is not worthy to make the change too soon if the change itself hurts you.
As a beginner in long run, i spent some time to change to mid-foot striking. It is good for my knee. But from what i read and experienced, two things more important than "midfoot vs heel " are:
1) don't land your feet before your body
2)take more step per minute (smaller steps) http://www.newbalance.com/performance/running/good-form-running/