Instructions
Head to Vermillion City. Go into the house to the left of the Pokemon Center and speak with the Fishing Guru. Tell him you love fishing. He will give you the Old Rod. Catch common Water-type of Pokemon such as Magikarp and Goldeen.
Go to Fushia City. Enter the second house to the right of the Pokemon Center to encounter a second Fishing Guru. Just like the first Guru, he will ask you if you enjoy fishing. Agree with him to obtain the Good Rod. Catch rarer Pokemon such as Tentacruel and Polywag.
Go to Lavender Town and head south to enter a guard house. Head through it to go to the Silence Bridge. Continue along the bridge until you encounter the Sleeping Snorlax. Enter the house to the south and meet the brother of the two Fishing Gurus. Tell him you love fishing. He will hand you the Super Rod, the best fishing rod in the game. Catch rare Water-type Pokemon such as Dratini and Dragonair.