Before Ruby & Sapphire revitalised the entire Effort Value and Individual Value system, Pokémon Red & Blue and Gold & Silver had a completely different system for calculation of stats. In this generation, each Pokémon could only have up to 15 for its IV, half what it has in later games, but the Effort Value system, commonly referred to as Stat Experience is vastly different.

Differences From Future Generations

What's the difference with this game? First off, rather than a limit of 252/255 in each stat, you can actually get up to 65,535 points in each stat with there being no upper limit to the amount of points you can put on your Pokémon. The values are then put through a massive calculation in order to obtain the actual stat value
For Hit Points
   floor((((Base Stat+IV)*2+(√(EV)/4))*Level)/100)+ Level + 10
For Others
   floor((((Base Stat+IV)*2+(√(EV)/4))*Level)/100)+ 5
Like the other generation, you can easily determine the stat difference between an untrained Pokémon and fully trained Pokémon simply by square rooting the values and then dividing by four. As such, the differences aren't as high so let's base this on a Dragonite that has been solely levelled up with Rare Candies and one that has been trained and levelled up completely in order to showcase the differences

 Dragonite #1Dragonite #2

With the values being so high, training is a bit different to the way you may be familiar. Rather than battling specific Pokémon to get the optimal stat points, the Pokémon you defeat actually give you the values based entirely on their very own base stats. These stats can be found in our Generation 1 Pokédex. This means that whenever you defeat a Pokémon, you will get values added in each stat. Due to this, you never have to worry about specifically training for each stat.

Hit Points Attack Defense Speed Special All Totals

Like the other games, the Vitamins work wonders in helping you get your Effort Values up. Like the other games, however, they do have an upper limit once again. This time, they will never add beyond the first 25600 that the Pokémon has in each stat. This makes them great to help start a Pokémon off in their strength

PicItemEffect on EVs
HP Up+2560 Hit Point EVs
Protein+2560 Attack EVs
Iron+2560 Defence EVs
Calcium+2560 Special EVs
Carbos+2560 Speed EVs

The best way to get your Pokémon up to 65,535 in each stat is to just keep battling various Pokémon in the wild. There's no specific trick to it, and levelling up your Pokémon to Level 100 should take care of the bulk of it, but if you wish to focus on certain stats as you go, the following are your best bets due to high stats in each stat and high (30% or above) encounter rates in the listed areas, but defeating the other Pokémon in the same areas will do no harm.

Potential Focus Pokémon

StatRed/Green(Jp)/Blue(US)Blue (Japan)Yellow
HP Slowpoke - Route 10/Celadon City (Super Rod) Slowpoke - Route 10/Celadon City (Super Rod) Slowpoke - Route 12/13 (Surf)
Attack Krabby - Route 6/11 (Super Rod) Krabby - Route 6/11 (Super Rod) Krabby - Route 10/25 (Super Rod)
Defense Onix - Victory Road Onix - Victory Road Geodude - Victory Road
Special Tentacool - Route 19/20/21 Tentacool - Route 19/20/21 Tentacool - Route 19/20/21
Speed Diglett/Dugtrio - Diglett's Cave Diglett/Dugtrio - Diglett's Cave Diglett/Dugtrio - Diglett's Cave

With that, your Pokémon will be EV Trained. However, rather than just at Level Up, there's another way to apply the Effort Values, so you can still train at Level 100. All you need to do is deposit your Pokémon into the PC and withdraw it and the Effort Values will be counted, so using Rare Candies isn't a massive issue.