First, take off the dead wood. This is the dry, unproductive stuff that simply takes up space and time. What clutter can you delete from your life so you can use that time for writing? What words, sentences, or scenes are cluttering your manuscript and slowing the pace? These are the parts that you can see you don't need. You might like them, but you don't need them. Get rid of the "dead wood".
Second, let your bush/life/manuscript breathe. Take off crossing branches and thin excess interior canes. Simplify when life or plots get too complicated. Sometimes you need a short break from a manuscript; sometimes you just need to trim the immensity down by focusing on one scene at a time.
Third, stimulate new growth. Cutting into green growth is not like trimming off dead wood. Emotion plays a part. This is where we need opinions from others, like a critique group, until we are confident and experienced in pruning. We can't always see what cuts need to be made to better our manuscript, so we rely on the experience of others.
Whether you want to branch out by taking more risks, or cut a thousand words from your work in progress, the pruning process can work to better a writer as well as a rose bush. It won't be long until you see the beautiful result.