A couple of weeks ago a friend of mine hit a deer while traveling on the freeway (the I-280). The damage was so extensive that insurance totaled it. Deer are most likely to travel onto roadways at dawn and dusk and are more often on roadways in Spring and Fall.
It is not always possible to avoid a collision with a deer but here are a few tips:
Scan the road for animals' reflective eyes, often visible at a great distance at night. Sometimes this is the only visible part of the animal until it is directly in your path. There is a good chance that if you see one deer there are others nearby, so keep alert. A deer normally freezes when it is in the headlight.
Travel in the center lane and avoid traveling at the same pace as other vehicles on the road.
Drive below the speed limit around corners and bends where your visibility is dramatically decreased.
Use your high beams where possible; they will illuminate more of the area that you are traveling through.
Some experts have suggested a long honk will scare deer off the road however that has not been proven.
If there is a deer on your path slow down as much as possible before attempting any evasive maneuver.
It is recommended that you keep your vehicles maintenance up to date, especially tires above recommended minimum tread as well as brake pads and rotors above recommended minimum thickness.
If traveling on a road with deer is a common route for you, and you are looking to purchase a new vehicle, look into ones that come equipped with a collision avoidance system. Check out the different options on Wikipedia.