Raising Pokemon: EVs

What are EVs?

EVs or Effort Values are points that go into a Pokemon's stats, for every 4 EVs in a stat, it gives 1 full stat point.

Every Pokemon start with 0 EVs, can gain up to 252 in a single stat like Attack for a gain of 63 stat points in that stat, and gain up to a total of 510 EVs among stats.

EVs can be viewed on a Pokemon's status screen by pressing Y (starting in Sun/Moon), a sparkling stat indicates it's maxed out at 252 EVs, while a blue graph as opposed to orange indicates the Pokemon has reached the limit of 510 EVs.

Where do EVs come from?
Every defeated Pokemon ingame gives certain EVs to any Pokemon you have in battle (including those affected by exp share) such as defeating a Yungoos giving 1 Atk EV.

The Vitamin items give 10 EVs to their listed stats each, but won't work on a stat that has 100 or more EVs already. Lastly, Isle Evelup stat drinks give 4 EVs per session (at rank 3).

What are EVs good for?
EVs can be used to manipulate the stats of any Pokemon to fit how you want them used, such as maxing out Speed and Special Attack on a special attacker like Alolan Raichu.

Due to 4 EVs=1 stat point, 2 of your 510 EVs will always be useless, which is why sets only list 508 EVs going into that Pokemon (most often 252 in two stats, and 4 in another)

Modifiers
Things that increase EV gain from battle are (all stacking) Power Items and the stats they raise are
 * Power Items: give an additional 8 EVs per KO in their respective stats
 * Pokerus: doubles all EVs gained by that Pokemon
 * SOS Battles: doubles all EVs gained
 * Weight-HP
 * Bracer-Attack
 * Belt-Defense
 * Lens-Specialk Attack
 * Band-Special Defense
 * Anklet-Speed

How to EV train your Pokemon
If you've shiny hunted you'll already be familiar with this method, but here it's a little simpler,

To get your Pokemon the EV spreads you want quickly, you combine the modifiers mentioned above and get into an SOS battle With SOS doubling and a Power item, 1 Yungoos would give 18 Atk EVs, with Pkrs added that's 32 EVs per KO.
 * 1) Give the Pokemon you're training the right Power item
 * 2) Get into a battle with the pokemon you're going to chain for (Locations of best Pokemon below)
 * 3) Use False Swipe and an Adrenaline Orb to get a chain going
 * 4) (With Pkrs) KO 7 Pokemon to max the stat (Without Pkrs) 14 KO's
 * 5) Repeat for the other stat(s) you're training

EV Training Locations
Here are the best Pokemon and their locations to chain for in Alola

HP

 * Poni Wilds-Surfing Ambush: Wailmer
 * Route 1-Grass: Caterpie
 * Trainer School-Grass: A-Grimer

Attack

 * Route 1-Grass: Yungoos (Day), Spinarak (Night), Grubbin, Pikipek (most available in other places as well)

Defense

 * Exeggutor Island-Grass: Exeggcute (Much better in SM)
 * Ten Carat Hill (Cave)-Walking: Roggenrola (has Sturdy)
 * Route 12-Grass: A-Geodude (has Sturdy)

Special Attack

 * Melemele Meadow-Grass: Petilil (Moon and UM only)
 * Trainer School-Grass: Magnemite (has Sturdy)
 * Brooklet Hill-Grass/Seaward Cave-Walking/Sandy Cave-Walking (USUM only): Psyduck

Special Defense

 * Route 1-Grass: Ledyba (Day only)
 * Route 2-Grass: Drowzee
 * Hano Beach-Surfing Ambush: Tentacool

Speed

 * Route 1-Grass: A-Rattata (Night only)
 * Verdant Cavern-Walking: Zubat, A-Rattata (Moon/UM only), Noibat (USUM only)
 * Trainer School-Grass: A-Meowth
 * Diglett's Tunnel-Walking: Diglett