Let us talk about pruning shrubs (multiple stemmed woody plants). There are two types of shrubs: ones that bloom on old wood (lilacs) and ones that bloom on new wood. For the ones that bloom on old wood (usually early flowering), wait till the shrub is done blooming before pruning (why sacrifice the flowers). The rest can be pruned now.
Most shrubs will be pruned because they are a tangled mess and you want to rejuvenate the growth.
1. Remove up to 1/3 of the plant. Remove the oldest canes by cutting them down to the ground. In three years, the shrub will have new canes and renewed vigor.
2. You can reduce the height by cutting the canes back. Cut above an outward bud using a bypass pruner and cut at a 45-degree angle.
3. If the shrub has a lot of growth in the middle, thin out the center by cutting the twigs back to the main cane. This allows air and light to get to the center of the plants reducing disease and insect damage.
Just doing these three things will make a teenager out of an old shrub new again.