EVs

EV's stand for effot value, they are gained when battling Pokemon. Each Pokemon that you battle gives out a certain amount of Effort Values. Effort Values are hidden from view though, so it is up to you to keep track of this.

Each Pokemon gain up to a total of 510 EVs. Every 4 EVs equals one stat point gained when you level up (if you gained 4 EVs of that stat while training). Out of those 510, 508 of them are usable (508 is divisible by 4 and 510 is not). However, each stat can only have a maximum of 252 usable Effort Values. That means you can max out 2 different stats. 252 EVs translates into 63 stat points. (63 times 4 is 252). Also, this can be supplemented by a nature. (A beneficial nature adds 10% more stat points overall, while a hindering nature takes away 10% overall. So a Pokemon with an Adamant nature gets 10% MORE stat points in Attack but 10% LESS stat points in Special Attack).
EV Train
HP:
~Shellos at Valley Windworks north of ignore the Buizel (+1 each)
~Gastrodons at Fuego Ironworks or Route 213 ignore Floatzel (+2 each)
~Gastrodons outside of Pal Park (+2 each)


Attack:
~Kricketune and Bidarel at route 212 (rainy route) (+2 each)
~Bibarels and Machop (2 EVs and 1 EV respectively) Route 208
~Machokes and Snovers at Acuity Lakefront (2 Evs and 1 EV respectively)


Defense:
~Cave with Geodudes and Hippopotas off route 214 (+1 each) (Ruin Maniac's Cave)
~Onix and Gravelers on Iron Island in the second room ignore Golbats (+1 Onix) (+2 Gravelers)
~Geodudes and Onix in the first room (Oreburgh Mines) (+1 each)


Special Attack:
~Gastly at the Old Chateau in Eterna Forest (+1 each) (Haunters +2) (Gengars +3)
*Need GBA Game in GBA slot and National Pokedex for Haunters and Gengars*
~Golducks surfing in the water at the Resort Area (+2 each)


Special Defense:
~Surfing any ocean/sea area for Tentacools (+1each)
*North of 8th gym town has been good ignore Pellipers* (Mantykes +1)


Speed:
~Raticates and Fearows Northwest of the Fight Area (+2 each) *name?*
~Zubats in a cave (+1 each)
~Golbats in Victory Road (in water, you only find Golbats) (+2 each)