Pokémon Red and Blue/Route 2 & 22

'These routes are a good place to collect more Pokémon. Route #2 (shown below) is full of Pidgey and Rattata, along with a specimen or two that are rarely found in this area. Remember to weaken a Pokémon in battle before using a Poké Ball on it, or else it will be able to break free. The first time you come through Route #2, head into Viridian Forest to continue your journey.'

Gary Awaits
If you want some quick EXP (and 280), you can challenge your rival in Route #22 by heading west towards the pond. But don't do it until you have a few strong Pokémon! Blue and Red players may want to wait until after Viridian Forest... Or skip it all together.

Yellow players, on the other hand, are at an advantage against Gary because even a low level Pikachu can incinerate his Spearow.