Learning to prune is more of a sensibility than an exact science. Once you have found your way through a few different types of shrubs, you begin to get a feel for what needs to be done. Study the growth habit of each plant; it will tell you a lot about how to shape it. Remember, if your shrubs are healthy to begin with, you won't harm them permanently with a little experimentation. Buy the best pruners you can afford. A good tool can be sharpened and repaired and will last a very long time. A pair of garden shears or kitchen scissors are perfect for shaping small-leaved shrubs as well as removing dead leaves and blooms.
How to Trim Shrubs
Stand back and examine the shrub. Never start cutting until you have decided what needs to be done. Have a picture in your mind of how it should look when you are finished. Decide whether the shrub will need a heavy pruning or a light trim. There is usually more than one way to trim a shrub. Some look better kept tight with low branching while others benefit from removing the lower limbs and exposing the bark. Take a little off at a time, and stand back and look again before proceeding.
Start by removing any dead or damaged wood. Air circulation is important; remove branches that are crossing or tangled within the shrub. Then trim back branches that are much longer than the others, but try not to cut everything the same length. Keep it natural.
Now begin the actual shaping. If you are new to pruning, just take a little off all over; ongoing maintenance pruning will help you get to know the plant. Avoid turning all of your shrubs into round balls. Pay attention to the natural form of each shrub and improve it.
Keep the shrub in shape. Once you feel comfortable with the shape and size of a shrub, trim it often. It is easier to clip a small branch here and there than to do a major pruning once a year.