Some scaly, needle-like evergreens, such as junipers and arborvitae, put on several growth spurts during the season. No matter what type of evergreen, almost all of its new growth will come from buds started the previous season. These are usually terminal buds, located at the ends of branches. Another common factor is that all evergreens are very reluctant to re-sprout from bare or old wood. Once you have opened up an area and can see the branches or trunk, it may not ever fill back in.
Yews are an exception, often filling back in when pruned back severely.
Broadleaf evergreens are handled the same as deciduous trees and shrubs. You can thin to control the height and size. On flowering broadleaf evergreens, prune right after they have bloomed. Rhododendrons will also profit from simply having the growing tips pinched back, encouraging side growth and better blooming. Korean boxwood can be lightly pruned at any time.