Some other general tips:
Were you hit an opponent has no effect on the amount of damage it does, so no head shots. Just aim for the biggest area, the chest and torso.
Conserve your arrows and don't spam them at the enemy. Try to only take a shot if you know it's going to hit; remember to completely flex the bow for maximum damage and range.
Have a melee weapon or a magic skill to fall back on if things get crazy. You never known when a bandit or pack of wolf's will ambush you in Skyrim!
There are 2 types of bows, long and short bows, I'm not sure what the difference is besides range, but I'm guessing the long bow sacrifices power for range, and the opposite for the short bow.
Always try to reclaim your arrows from fallen foes, every little helps.
Happy Hunting.
Longbows do more damage but take more time to draw back the arrow.
Shortbows vice versa.