ExplanationWhat are EV's?
EV's (Effort Values) are points given by certain Pokemon. Each pokemon can obtain a total of 510 EV's 225 per stat, and for every 4 EV's you obtain 1 stat point. Stat points can be described as a pokemon's Health or Attack.
GuideEvery time you faint a Pokemon it will give you a certain amount of EV's that to toward one of the six stats. Since you can evenly half the max amount of EV's your Pokemon you can get, most people would train 2 different stats to its Max. Once you start training one EV for a certain stat, do not train another stat untill you are satisfied with you EV's, if you do it will not be as strong as it could be. If you encounter a Pokemon that does not give the amount/type of EV's you want, run from it. Your Pokemon DOES gain EV's when it does not level up, but does not tally your stat points UNTIL level up. If you want a list go here:
http://www.serebii.net/pokedex-dp/sattack.shtml