Before you even ask, I'll say it. EV's, and IV's do not matter to me. This will generalize around Leaf Green

Kanto Gym Help an Training Montage
Updated When I Feel Like It

NPkmn: New Pokemon Introduced In The Area

Level: What Level All Pokemon Should Be At Before You Leave Area

*: Will Be In Main Team

-: Pokemon That You See, But DON'T Catch.

Part A, On Toward Viridian Forest

Pokemon Inroduced: 10
Pokemon You Will Have At End: 12
Pokemon Seen At End: 14

<Town Guides Later>

~Route 1~
- NPkmn: Rattata, Pidgey
- Level: 5

<Town Guides Later>

~Route 22~
- NPkmn: Mankey*
- Level: 5

<Town Guides Later>

~Route 2~
- NPkmn: Caterpie, Weedle
- Level: 10

My Best Fitting Team At This Point:
(Starter), Mankey, Caterpie, Weedle

What To Do:
Level Up Caterpie and Weedle to Level 10, so that you can get them out of your team (if you want, recomended)

Level Up all Pokemon to 10 BEFORE entering the Viridian Forest.

Pidgey And Rattata:
They go into your team depending on you. If you want them, add them. But for this point just catch them. You'll evolve them later.
------------------End Of A

Part B, Viridian Forest and Pewter City

Pokemon Introduced: 5
Pokemon You Will Have At End: 15
Pokemon Seen At End: 16

~Viridian Forest~
- NPkmn: Pikachu*, Metapod-, Kakuna-
- Level: 16

<Trainer Guide Later>

~Route 2 Cont.~
- NPkmn: Nidoran M* Nidoran F*
- Level: 20

<Town Guides Later>

Best Fitting Team At This Point:
(Starter 2nd Evo), Mankey, Nidorano, Nidorana, Pikachu

What To Do:
Get the two Nidoran's to the same level as your starter and Mankey. Level 20 is high, but it will set you up for the rest of the game easily.
------------------End Of B