After you meet Mr. Fuji at the top of Pokémon Tower and get the Poké Flute, you can go south from Lavender Town to Route 12 and wake the sleeping Snorlax.

Explore Route 12

You can go south from Lavender Town into Route 12, go south into the Guard House, go upstairs and talk to a girl there to get TM50 Roost.

Go downstairs and go south. Go east and you can talk to the Fisherman to battle Fisherman Ned, who has a level 27 Staryu. You get 1080 Pokédollars and 3 Poké Balls for winning.

Go south from there, and follow the path. You can battle Fisherman Chip, who has a level 27 Poliwhirl. You get 1080 Pokédollars and 3 Poké Balls for winning.

Go northwest to find a Lure.

Go south from there, then east, then south. You can battle Fisherman Hank, who has a level 27 Magikarp, a level 27 Seaking, and a level 27 Poliwag. You get 1080 Pokédollars and 3 Poké Balls for winning.

To the right of Hank, there is a Repel.

Go south and follow the path. You can battle Fisherman Elliot, who has a level 27 Gyarados and a level 27 Magikarp. You get 1080 Pokédollars and 3 Poké Balls for winning.

Go south from there, then when the path splits, you can go east to battle Ace Trainer Zach, who has a level 28 Tangela and a level 29 Onix. You get 2900 Pokédollars and 5 Ultra Balls for winning.

To the right of Zach, there is a set of 3 Ultra Balls.

If you try to go any farther south, you find your path blocked by Snorlax. If you met Mr. Fuji at the top of Pokémon Tower, you can check on Snorlax to wake it up. When you wake it up, you have to battle it, and you have to defeat it within five minutes. After you defeat it, you can try to catch it.

After the path is opened, go south and you can battle Fisherman Andrew, who has a level 36 Tentacool and a level 36 Kingler. You get 1440 Pokédollars and 3 Poké Balls for winning.

Go south and go into the house. Talk to the old man there. If you say that he is "Mr. Dazzling", you get TM32 Dazzling Gleam.

Go south, talk to the Poké Maniac if you wish (he won't battle you), then go south and chop down the tree on the left. Go west and you will battle Rocker Luca, who has a level 36 Electabuzz. You get 1008 Pokédollars and 3 Poké Balls for winning.

Go west to find a Water Stone. You can use it to evolve certain pokémon.

Go south and you can battle Camper Justin, who has a level 35 Nidoran♂ and a level 35 Nidorino. You get 700 Pokédollars and 2 Great Balls for winning.

Go east to find an Awakening.

Go southwest and you can battle Coach Trainer Priya, who has a level 38 Butterfree and a level 39 Clefable. You get 3900 Pokédollars for winning. After the battle, you get TM59 Dream Eater.

Go south, then west, and chop down the tree to reach some grass, where you can catch Pidgey, Pidgeotto, Bellsprout, Weepinbell, and others.

Check in the south part of this grassy area to find a Max Lure.

Leave the grassy area and go south on the pier to reach Route 13.