Things to know – After a fresh snow fall do not directly follow the tallest guy in a group. The snow he knocks off the trees will land on you and inevitably will go down your neck. Lesson learned.
More things to know – Do not pack your cliff bar in an outside pocket. Just when you need it, at perhaps an hour into the run, you will discover that it is rock hard. Your teeth will not be up to it. If you had broken it into bits before the run you could have put the bits in your mouth to warm them up before trying to chew them. Or better yet, put them in an inside pocket. As it is you have no fuel but you must struggle on anyway. Lesson learned.
One last thing to know – Do not leave the end of your water bladder hose hanging outside where it normally goes. It will freeze and then you will have no water for the rest of the run. This could happen as early as 20 minutes into a run. Dehydration will occur. Instead stuff the end inside your jacket where your body heat can keep it thawed. Lesson learned.
All these lessons can be reinforced with a 2.5 hour icy trail run in the mountains, or if time is not on your side you can re-read this post in less than 30 seconds.