Determine the size you want to cut the boxwood down to, so you know how much of the growth to remove. Ideally, prune the shrub so its base is wider than the top, so plenty of sunlight reaches the growth near the base. Locate tall, wayward, low-lying and crossing branches, along with those that are damaged or diseased. Selecting the branches you wish to remove beforehand reduces time during the actual pruning process.
Cut back dead, diseased or damaged branches from the shrub using sharp, sterilized pruning shears, or use a pruning saw if the wood is thick. Make a 45-degree cut to sever a section of the branch from the remaining wood, or snip off the entire branch if the damage is extensive and irreparable. Cut leggy or thin branches from the base of the shrub.
Cut low-lying branches that extend beyond the canopy of the shrub. Also cut wayward branches that extend beyond the sides of the main growth. Locate rubbing branches within the interior of the plant, and snip these off since frequent rubbing damages bark, making the branches susceptible to disease-spreading organisms. Clipping branches within the interior also improves sunlight penetration and air circulation to the shrub.
Cut the tallest branches down to one-third their length. Use sharp, sterilized pruning shears to make straight cuts within 1/2-inch of an outward-facing bud on the branch. Form the cuts at 45 degrees.
Step back and review the pruning attempt. Walk around the shrub, pruning sections of growth you missed, so the shrub has a symmetrical and uniform appearance. Use hedge clippers to trim tall growth on the canopy, giving it a neat appearance.
Collect the clippings from around the base of the shrub and place in a tarp or wheelbarrow.