Where to cut above a node
When shortening a suitable stem, keep a healthy node on the plant and cut on its tip side.

Before you start
Follow the stem you plan to shorten. A node is the point where a leaf or bud joins the stem. Find one at the length you want to keep and make sure it belongs to that stem.
How to do it
Cut a little past the node toward the tip you are removing. Leave the node, the bud and the stem below it intact. Use sharp shears for one clean cut.
When to stop and recheck
If you cannot see the node, or you might be cutting a leaf stalk or the plant's only growing point, stop. Watch the kept node for new growth before shortening more stems.