It depends on what gym leader you are one. If you are in Violet City, you must defeat the first gym leader and travel to Azalea town to defeat the rocket grunts in the slowpoke well. Usually, just defeating the gym leader of your current city is all you need to do.
go to the next gym leader.
Go to Blackthorn city. The gym is there
go to the seventh leader. -_-
you just go north of blackthorn city and beat the gym leader
Go to Mahagony Town.
clainwood
USE YOUR MAP and it is near the water gym(gym leader misty)
first get a ice type Pokemon then go threw the whole gym face gym leader and get the badge
You go inside the gym, and there is usually a maze you have to get through to be able to fight the gym leader. After that, you just walk up to the leader.
go to vilet city.
you have to go to funchisa city in kanto
Go to the next city and battle the next gym leader (gym leader Fantia located in Harthome City)