Make sure the implements you are using are clean and sharp. This both ensures fewer blisters and helps prevent plant injury. Sharpen blades at a 45-degree angle with a file by swiping them across the sharpener at least 10 times.
Create a form for you to follow by shaping a piece of galvanized wire into the size of ball you are going to make. Use twist ties to fix it to the top of the bush.
Prune out extra stems and leave one strong central leader or trunk. This will allow you to have a fully round ball that stands out. Alternately you can prune a bush into a dome on the ground but the bottom won't be fully round.
Remove lateral growth on the main stem up to the level where you wish the ball to begin with pruners. Snip off shoots that are growing outside the wire form to just above a leaf. Move the form as needed for different angles of the ball but attack one facet at a time.
Take off the wire form when you have roughed out the shape of the ball. Use the shears to smooth the shape and remove errant leaves.
Provide superior care to the bush while it recovers from the severe pruning. Keep it moist but not soggy and fertilize it with a balanced fertilizer the following spring according to the product instructions.
Reshape twice a year in early spring and again in late summer to early fall. Keep the ball in the original size or allow it to expand as you simply trim to keep the shape.