Three groups of oak trees exist: white oaks, red oaks and live oaks. Just as with other deciduous trees, oaks must be trimmed to remove dead, diseased or damaged branches, to maintain/control the size of the tree within your landscape design, and to thin out the crown of the tree.
Take caution as to when you trim your oak tree, due to oak wilt disease, which kills thousands of oak trees in a single year. Due to how this disease is spread, only trim and prune oak trees during the "safe period," which is from November through March.
Trim away damaged or diseased branches immediately. Make a clean cut (so that the tree can heal properly) at the point of the break. (You can also choose to remove the entire branch.) Dead or diseased branches should be removed completely. Remember, do not put diseased plant material in your compost bin.
View your tree from all angles to determine if it is rubbing on a roof, structure, or if it is imposing near a walk way. Remove the branches by locating the branch collar (this is on the underside of the branch where it connects to the trunk) and the branch bark ridge (this is on the topside of the branch where it connects to the trunk). Make your cut right in front of the branch bark ridge and the branch collar--do not leave a stub, and do not cut into the branch collar or the branch bark ridge.
Visually examine the crown of your tree, looking for deadwood and cross-over branches. The removal of dead twigs and branches is known as "thinning of the crown." When your tree is young, you will be able to do the thinning yourself. However, as the tree matures you will likely need to have a professional tree service do the thinning for you. Professional tree services know what branches/limbs to trim to maintain the appearance and integrity of the tree. They also have the equipment required, and they are used to working at the heights involved.