Open your crafting table (or crafting grid).
Place 2 sticks in the middle column: one stick in the top-middle slot and one stick in the middle-middle slot.
Place 3 string in the top row: one string in the top-left slot, one in the top-middle slot, and one in the top-right slot.
Place 1 piece of tripwire hook in the center slot (only in Java/Bedrock versions that use a tripwire hook ingredient; otherwise use 2 additional string as required by your version).
Take the fishing rod from the output slot.
If you do not have the required items, gather:
Sticks (wood planks + crafting)
String (spider drops or cobweb/string sources)
Tripwire hook (iron ingot + iron ingot + string, depending on your edition)