If a deer runs out in front of your car, stay calm, and try not to further endanger yourself, your passengers, other traffic, or the deer as you would in any other collision situation.
But there are several preventative steps you can take to avoid running into deer in the first place.
The first is being aware of the season. Deer are most prevalent in June, when young fawns are on the move, and from October through December (mating season).
A good thing to remember during these times, and always, is to lower your speed in heavily deer-populated areas; if you see deer signs, heed them.
And keep your eye especially keen during the dawn and dusk hours, when deer are most active.
Most car-deer collisions happen during these low-light times of day. If you do hit a deer, some states allow you to keep the carcass.
Whether you want venison for dinner or not, contact the authorities and alert them about the hit immediately.