Running on Ice !
Possibly the main reason why runners take a tumble during winter is ICE. A major hazard especially when covered with snow and unseen. Wear a sticky rubber studded fell shoe. Observation and recognising spots where ice may form can help prevent an accident. Watch out for signs such as does the area look at if it was boggy, are there any rivers nearby, does it look as if water has run-off across the path, is there a hole in the ground that may have contained water. There is current view in the UK to attaching spikes to your shoes or using 'O' shoes with dobs which may help, but this has an environmental impact of scratching rock, just like the issues regarding crampons and dry tooling in climbing. Understanding your environment is better than damaging it !