Deer in my parts are extremely common. There is no real key to avoiding them except for not driving during sun up or sundown or certain times of the night, pretty much like RAAM said. Deer activity seems to peak in the evening about an hour after sundown and will usually cease 2-4 hours after sundown then they start to move in the middle of the night albeit not much and then again when the sun is about to rise. So you have small windows here and there.
Amazingly with all the driving i do during those times I have only hit one deer and it was at like 7am in the summer and I was going about 5mph it looked at me and just ran into my truck, dumb thing. I have hit a Mtn lion doing about 80mph once it was like hitting a brick wall, if it were in my Fiesta the car would have been toast.
Deer whistles don't work. I think the theory was they emit a sound, liken to a dog whistle, and deer will respond to it. Usually deer are so desensitized to vehicle traffic they simply wont move until its too late for them and us.