Head south from Cerulean City on Route 5 to reach the house in the center of the route. The old woman in the house will give you a Cleanse Tag, which will help keep wild Pokémon away from you.
Get the old woman's Cleanse Tag
You'll have to drop down from the top to get to this house. The old woman will give you a Cleanse Tag which, when equipped, will reduce the number of wild Pokémon encounters you face. After Route 5, cut west through Saffron City and Route 7 to get to Celadon City.