Instructions
Capture a Doduo. Doduo can be found as a common Pokemon in tall grass along routes 16, 17 and 18, as well as in Safari Zone areas 1 and 3. Capture Doduo using the regular tactic of fighting it until it reaches low health and throwing Poke Balls until it is captured.
Use your Doduo regularly in battles. At the end of every battle, it will gain experience points and level up.
Stop your Doduo's evolution. At Level 31, Doduo evolves automatically into Dodrio, a larger and more powerful form with three heads. You must stop this evolution by pressing the "B" button every time it levels to cancel evolution. Alternatively, you can walk to Route 10 and find an Everstone sitting on the ground in an unopened Poke Ball. The Everstone is an item that prevents evolution in the Pokemon holding it.
Continue using Doduo until it reaches Level 37. The game will inform you that your Doduo wishes to learn Drill Peck. Choose a move to overwrite, and your Doduo will now know the attack. Stalling your Doduo's evolution allows you to teach it Drill Peck at Level 37, a full 10 levels before Level 47, when Dodrio is able to learn it. You can now evolve your Doduo into Dodrio.