Head for Viridian Forest.

After an afternoon spent travelling to and from Viridian City, delivering a package from the Pokémart to Professor Oak, saying goodbye to your mother, you find yourself standing on the outskirts of Viridian Forest with your new Pokédex, a bag full of Pokéballs, potions and antidotes, and of course, your new companion, Bulbasaur on your hip.

The forest is full of insectoid Pokémon, and worse, nerdy Bug Catchers. But it's the only way to get to Pewter City, and the first Pokémon Gym.

Additionally, you could also train or try to catch a second Pokémon. You never know what'll come in handy in one of these gyms.