Pokémon Red and Blue/Route 2 & 22

'These routes are a good place to collect more Pokémon. Route #2 (shown below) is full of and, 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.'

Rival Awaits
It's a good idea to take some time and train your Pokémon in Route #22. If you're playing the Yellow version, you'll have the opportunity to catch a Mankey. Be sure that you do. Otherwise, be sure to pick up whichever Nidoran is more prevalent in the version you're playing, both if you're trying to complete your Pokédex. If you also stumble upon a Spearow, it makes a nice addition to your collection. If you would like to earn extra EXP (and 280), you can challenge your rival in Route #22 by heading west towards the pond along the top path. Before you do, make sure that you have a few strong Pokémon, and that they're fighting fit! You may wish to wait until after you've traveled through Viridian Forest to conduct this battle... or skip it entirely.

If you beat your rival, you can head back to Pallet Town to get 5 Poké Balls for free from Professor Oak in his lab (but only if you have not purchased any Poké Balls yet, so it's really not worth the hassle of fighting your rival with only your starter Pokémon).

When you're done in Route #22, make your way back to Viridian City and exit through the north path to reach Route #2. Much of this route is inaccessible to you early on in the game, but that will change in time. For now, your only concern is reaching the entrance to Viridian Forest. Don't bother hunting for Caterpies or Weedles out here; they're more plentiful in the forest.

Rival Battle #2
Your rival has improved marginally since Pallet Town. In Red and Blue, he's toting a Pidgey in addition to his starter; in Yellow, a Spearow. You will also want to have some new Pokémon at your disposal.

The first order of business is acquiring a Spearow, since it's right here on Route 22. Anyone not using Charmander needs to acquire a Spearow. Training it to L7-L8 will be sufficient. After that, go to Viridian Forest and capture a Pikachu. All parties want to do this, because Pikachu can counter your rival's new Pidgey (as well as 2/3 starters). Level Pikachu up to L9 for Thunder Wave.

Now, the strategy. Your rival always leads with Pidgey; send out Pikachu and K.O. it in 2-3 Thundershocks (preferably two). If your rival chose Bulbasaur, switch to Spearow and Peck until Bulbasaur falls; if Squirtle, keep Pikachu in and Thundershock repeatedly, sending in Spearow if Pikachu falls. Finally, Charmander has no available counter yet; you'll have to rely on a small degree of strategy, namely Pikachu's Thunder Wave. Paralyze, then attack until one Pokémon faints; if Pikachu goes down first, Spearow can finish it with ease.

In Yellow version, your rival has Spearow and Eevee. Pikachu will destroy Spearow without any difficulty whatsoever, and Eevee is best handled by catching a Mankey on Route 22 and raising it to L9 for Low Kick.