Step 1: Buy pipe-shaped insulation.
Step 2: Turn on the hot water tap until the water is actually hot.
Step 3: Put insulation around the hot pipes.
Step 4: Pull off yellow tape and press the insulation so that the adhesive sticks. (I bought the "expensive" insulation - the cheap stuff didn't have adhesive but looked harder to work with. The expensive stuff was $0.83 each.)