keeping your visor shut
A lesson which I had the misfortune of learning first hand is that, whenever under the effects of a bad cold or flu, you should never open your visor whilst traveling at speed.
As you may have figured I once had a bad case of the flu, and consequently was riding with a sniffly nose. Minutes after reaching the highway I felt a small trickle from one of my nostrils. If this happens to you - UNDER NO CIRCUMSTANCES - attempt to open your visor and wipe it with your glove. I do not have a solid understanding of hydrodynamics but I can inform you of the weird tendency for whatever was descending from your nose to instantly be blown upwards (towards your eyes but more typically straight onto the visor) and seriously impair your forwards vision, possibly causing you to spear off the road/track/pavement etc.
Just thought youd like to know