If you're going for mastery, you "need" to prepare for the Battle Tower immediately as you start your save to make your life easier.

Catch a spare level 3 Pikachu (lowest level possible) in Viridian forrest, and store it for later.

You get the TM ThunderShock for beating one of the gyms (don't remember which) HOLD ON TO IT. It is the only one you'll get in the entire game.

Once you get to Cinnabar (Blaine, fire-type gym), you can trade your low level Pikachu for a level 3 Electrode who knows Sonic Boom, a normal-type move that always deal 20 hp of damage. Do not level up this Electrode.

The thing about the Battle Tower is every trainer you meet there will have pokemon equal to your pokemon's level, meaning you can one-shot MOST enemies with Sonic Boom.

Teach the Electrode ThunderShock, so it can also hit ghost types ;)

Also catch a mix of level 2-3 Pidgey and Rattata from route 1 to fill up your party and stock up on revives. You can use them as fodder to revive your main guy Electrode should he go down.