A systematic review published in 2012 investigated the available scientific literature to identify what were the main causes of injury in runners.

The evidence suggested 60-70% of all injuries were a result of training errors. The main causes were

- Excessive mileage (total weekly mileage).

- Increased frequency of sessions (more sessions per week).

- Increases in speed (interva / tempol training / sprints / hills).

- Changes in terrain (changes from flat to hill work or cross country / off road).

An interesting comment caught my attention "In a review of the etiology and prevention of and intervention for overuse injuries in runners, Hreljac (2005) concluded that the causes of all overuse running injuries could be classified as trainiing errors, and thus, all overuse running injuries should be preventable". 

In simple terms the authors believe overuse injuries are completely preventable. This is an absolutely massive statement. 

A simple strategy that I’ve found helps is keeping a training diary and knowing how to analyse the weekly workload. Look for increases in the training errors above as well as cross referencing for any pain, aches or niggles. This is one of the most important tools in injury prevention for the average runner. 

References: 

Rasmus Oestergaard Nielsen, PT, Ida Buist, PhD,Henrik Sørensen, PhD, Martin Lind, PhD,Sten Rasmussen, MD.
Training Errors And Running Related Injuries: A Systematic Review. The International Journal of Sports Physical Therapy. Vol 7, No 1: 58-71. 

Hreljac A. Etiology, prevention, and early intervention of overuse injuries in runners: A biomechanical perspective. Phys Med Rehabil Clin N Am. 2005;16(3):651-67, vi.