Even though Pokemon FireRed was introduced in the 3rd Generation of Pokemon, Effort Values (EVs) actually still exited back then. Like the current Pokemon games, all Pokemon can earn a maximum of 510 Effort Values to better improve their Stats, with 252 Effort Values being the highest divisible cap to one specific Base Stat. Like all Mainstream Pokemon Games, the main way to earn Effort Values is simply by defeating Wild Pokemon. All Wild Pokemon will give your Pokemon a certain amount of Effort Values to a specific Base Stat when defeated, the type depending solely on the Wild Pokemon's Highest Base Stat Category.
Because of this, players can usually farm Effort Values of a specific Base Stat simply by going to a certain area within the game and defeating the same Wild Pokemon over and over again. This strategy can even combined with PokeRus to earn twice as many Effort Values for each Wild Pokemon they defeat! If you're looking to farm Speed Effort Values, head to Route 1 and defeat one Pidgey (50% Encounter Rate) after another. For each one you defeat, your Pokemon will earn +1 Speed Effort Value. That will be +2 Speed Effort Values if your Pokemon has PokeRus!