Viridian Forest and Pewter City
In Viridian Forest, you can capture the following pokemon:
weedle When you first enter the forest, go left and explore the area. Be sure to have a few pokeballs on hand. When you get the items around that area, go back to the entrance of the forest and go right and face the trainers. FACING TRAINERS IS A MUCH FASTER WAY TO TRAIN YOUR POKEMON. Follow the path and when you finally reach the last part of the forest and you beat the bug catcher there, you are ready to catch pikachu.
THIS IS HOW I CAUGHT PIKACHU:
When you are in the area above the last bug catcher, walk around here. You may have to wait a long time before you face even one pikachu. I had to come face to face with about 30 pokemon before i saw one pikachu. But the wait is worth it! Pikachu Rules!!! When you capture pikachu, go up to Pewter city.
Pewter City:
This is where you have to face your first gym trainer, Brock. To beat Brock (who uses rock pokemon), it's slightly easier to use squirtle or bulbasaur. I managed to beat him without any of those. Brock uses onix and geodude. After you beat brock you get the boulderbadge. This is your first step towards the pokemon league!!!
Now that you have beaten brock, pay a visit to the museum (above the gym). When you do that, go right and face all the trainers until you reach Mt. Moon.