Many evergreen trees need little, if any, pruning. Most of the time you can get away with simply removing the dead or broken branches. Evergreen shrubs should be pruned occasionally to keep them from growing too large for the area they are planted in. Take caution that you do not over prune evergreens. If you cut past the green needles, the tree will not be able to grow new needles. The exception to this is the Juniper, which can withstand heavy pruning and is often used to create topiary's.
Thin or prune your evergreen in late winter or very early spring before new growth has begun. If you miss this window of opportunity you may still prune in early June before the new growth has had time to harden.
Cut off dead or broken branches close to the trunk. Cut from the bottom of the branch, 1/3 or 1/2 of the way through. Then cut down from the top until you meet the bottom cut. This will prevent the bark from ripping as the weight of the branch pulls it off.
Prune your evergreen a few times per growing season if you are trying to maintain a certain shape or size.