Do open up the plant with thinning cuts. Just trimming back branch tips, either with manual pruners or electric shears, results in dense foliage at the top of a shrub and a tangle of weak, leafless branches at the center. Thinning cuts remove whole branches down to the base or take
off large sections of branches back to a main stem, allowing light and air to reach the center of the plant and encouraging healthy new growth throughout. Remove the thickest, oldest wood first before moving to younger stems.
Don't remove more than one-third of a plant's mass in a year, to keep it vigorous and looking good.