FYI- this guide is based on my opinion
EV training is easy. Different effort values are gotten from different pokemon, one stat can have a max of 255 EVs. Every 4 EVs gotten gives one stat point. If you're careful and if you count, you can put 252 EVs in two stats and give the remaining 6 EVs to a different stat (But I consider this a pain in the ass, since if you're not careful, you can end up not adding the full 63 stat points). Theres only a few things you need to become a EV trainer
1) Pokerus, a virus which can be spread. Pokerus doubles the EV'd gained.
2) Either the Macho Brace or Power items [Power items are better, they give 4 EV's, Macho Brace only doubles them]. Power item can be bought for 16 BP each. Heres a list of the power items and what they do
Power Anklet Lowers Speed, increases EV for Speed
Power Band Lowers Speed, increases EV for Sp.Defense
Power Belt Lowers Speed, increases EV for Defense
Power Bracer Lowers Speed, increases EV for Attack
Power Lens Lowers Speed, increases EV for Sp.Attack
Power Weight Lowers Speed, increases EV for HP
3) The final thing you need is locations of the pokemon EVs you need - Here is a list of what I consider the best for EVing
Hit Points - Cowgirl Shelly, she's at the bottom of Solaceon Town, before you go throw the quicksand ramp; she has 5 Bidoofs which give 1 EV each. Wild Chansies can also be battled, but Shelly is probably the fastest way to EV HP.
Attack - Gyaradoes on Route 229 when you fish with super rod [Gyaradoes ALWAYS show up]. Machop and it's evos.
Defense - Iron Island everything except Golbats. Geodude, Graveler, Onix, ect.
Sp Atk - Go the the Old Chateu, it's the best place, everything that pops up there gives Sp At EVs [Gastly, Haunter, Genger].
Sp Def - Tentacools, Tentacruels, surf above Sunnyshore.
Speed - The bridge connecting Eterna City to the forest, a fisherman with 6 Magikarps[each Magikarp gives 1 speed EV](IMO, BEST place for speed). Zubat, Golbat also give speed EVs.
You might think that "aww, they only give 1 EV." But, don't worry if you have Pokerus, a Power item, and a Pokemon who gives 1 EV, it ends up as 10, so you only need to battle 26 of those to max out EVs. Check Serebii [ http://serebii.net/pokedex-dp/ ] for lists of other Pokemon who give EVs to the stats you're EVing.