This guide is for those who know it all except for possibly (unlikely) what I am about to type about EV spreads. I abridged it because no one will read it otherwise. If you're an expert, why waste your time reading a long guide? To create expert EV spreads that are beyond the already egregious skills of you competitive Pokemon masters of Sppf, follow the following steps so long as they apply to your Pokemon (1 and 7-9 apply to all). A link to the unabridged portions follows each step.
1.)Think about what you want your Pokemon to do. Set a useful goal for the Pokemon first. Make sure it's possible to achieve through damage calculators such as: http://ownpurpose.com/libelldra/damage_calculator.html Choose the nature you think you'll need at this stage. Unabridged.
2.)Find something important to outspeed. If your Pokemon is too slow or a wall like Cresselia, this is less important. It depends on your goal though. There's no point in putting speed on wallish Pokemon like resttalk Cresselia or Crocune since (a) it's useless to their purpose and (b) it will be useless nearly every time. They get more use by putting those EVs in defenses (including HP). Maximizing speed when the spare EVs are useless elsewhere is fine (e.g. CB Weavile). Unabridged.
3.)Find something important to NHKO. OHKO, 2HKO, OHKO with SR, etc. Very important for sweepers, somewhat important for tanks, and less important for walls. It depends on your Pokemon's purpose. Maxing the offense of sweepers is fine. Stuff with awful offense generally ignore this step. Unabridged.
4.)Find something important to survive. Very important for tankish and bulky sweeperish Pokemon. For Pokemon like Snorlax and Skamory, maximize their defensive potential in accordance with your original goal. For frail Pokemon like Weavile and Gengar, you generally don't need to bother with this since it will be (a) a waste of EVs to survive something or (b) they won't be able to survive it anyways.
5.)If you want to maximize defenses, max HP first. If it has loads of HP relative to its defenses, you don't need to max it (e.g. Snorlax, Blissey). If it doesn't, you must max it (e.g. Dusknoir, Rotom-A). If it's in-between (e.g. Latias, Metagross), you can go for a lefties point, but only do so if it (a) provides better defense (rarely happens) or (b) provides those smidgen of EVs necessary to KO or outspeed a threat in accordance with steps 2-3. If your Pokemon is weak to SR or takes neutral and runs items that do not affect its health (Choiced item, Expert Belt, Berry, etc.), don't make its HP divisible by 4 if the former and don't make its HP divisible by 8 if the latter. Those rules don't apply if you have Sandstorm or hail on your team and your Pokemon is weak to it. Don't bother with "minimum Life Orb recoil." So long as HP isn't divisible by 10, you're fine.
6.)In maxmizing defenses, put EVs in defense last. For all Pokemon but Pokemon like Blissey and Snorlax, this is true. To maximize defenses, find what combination of the EVs that you still have left split between HP and defenses gives you the best defensive potential.* Note that 128 / 128 is often bad.
7.)Be economical. Use the combination of EVs which gives you the most out of them.....EVERY TIME!!! That means you may find that your originally intended nature must be changed at this stage of EVing or that you can do more with your EVs than your original goal. Consequently, your EV spread and maybe goal needs to be changed. If so, go back to step 1. Also make sure each EV placement has a reason backing it. Stuff like "enough to outspeed x, maxed HP, enough to OHKO y, rest dumped in Defense" is fine provided outspeeding x, max HP, and KOing y is useful and viable.
8.)Extra EVs and gaining them. Use extra EVs to hit jump points. Or if you need or want extra EVs, hit a jump point in one stat you originally had maxed or hit the nearest jump point you can while still doing something specific in accordance with step 2-4 and your original goal. The former is the usual situation, hence splits like 176 / 80 or 216 / 40. Hitting lefties points gives extra EVs, but they have been discussed already. Also, use 252 > 255. Unabridged.
9.)Remember: think > goal > specification > optimization > bonuses. Stop in the chain when you run out of EVs, obviously. Speed is usually the first step of specification, but all this has already been discussed. A combination of experience, your team, knowledge of whether a Pokemon is outclassed at what it's doing or of whether it's doing too much to be effective, and Shoddy statistics/Smogon's movesets will help you determine "usefulness," "stuff to aim for," and "viability." Also, useful speed tiers and Smogon's OU, Ubers, UU, and Little Cup speed tiers.
I humbly submit this to our CRMT guide collection even though no one will read it once it goes there. If it's a hit, I'll continue with my "Abridged Series for Competitive Pokemon Masters" in a future installment. I wonder if our persistent, yet-to-be-discovered troll friend will rate this five stars? ^_^
This will explain what I mean by defensive potential (VERY similar to "Statistical (Special) Defense") and will give examples of EV spreads. Only read this part if you need examples, don't know what in the world defensive potential is, or are simply interested. Reading this appendix makes the guide much less abridged. Note that the concept of defensive potential is slightly flawed due to game rounding, and so it should not be used when making very precise spreads.
Determining defensive potential (e.g. determining whether one combination of HP and SDef is better than another combination of HP and SDef on the special side) is quite simple. Multiply your Pokemon's HP stat by one of its Defense stats to get a number. Try a different combination of HP and that same defensive stat then multiply them again. Compare the two numbers: (the larger number x 100 / the smaller number) - 100 = combination that created the larger number is w% better than the combination that created the smaller number.
Or you can use: the smaller number x 100 / the larger number = combination that created the smaller number takes hits w% as well as the combination that created the larger number. Offensive potential (e.g. determining whether a given SAtk stat and move is better than the same SAtk and another move (or a different SAtk and same move) on the special side) is similar and is compared with the exact same formulas. The numbers you use are found by multiplying an attack stat by the base power of the appropriate move. In both cases, the larger the number you get from multiplication, the better the defensive or offensive potential is.
Examples of EV spreads
Jirachi @ Leftovers
-Zen Headbutt/Iron Head/Ice Punch
I start by figuring out what I want it to do. It's obviously supposed to be bulky. Taking two DD LO Salamence Outrages and an Adamant CB Dugtrio EQ (to get off one last Wish if timed right) isn't a bad idea either. To start, I max the HP. I then find how many EVs I need to survive that from an Adamant LO Salamence by using a damage calculator, since I know it will hit harder than Dugtrio. I start by maxing defense and using an Impish nature and check the damage. I then lower my defensive EVs by and repeat again and again. Doing this, I find I need an Impish nature and 140 EVs in Defense to survive this after SR damage.
Since Jirachi reaches 236 Speed with a neutral nature and 0 EVs, a reasonable speed to aim for is 245, outrunning both Jolly Max speed Tyranitar and those trying to outrun it by 1 point. This requires 36 EVs. I then dump the rest in SDef to soften special attacking blows, giving: 252 HP / 140 Def / 80 SDef / 36 Speed. From experience, I know Jirachi can survive attacks from LO Gengar given enough EVs. I check to see how close Jirachi is to surviving it. Jirachi survives it well, so I see how well it survives consecutive Shadow Ball and Hidden Power [Fire] (after Jirachi switches into an obvious Shadow Ball or Focus Blast, HP [Fire] would be Gengar's next reasonable move).
It turns out it barely survives (outside of SR). So, I play with the EVs between HP and SDef until it survives it the best it can. I do not lower the HP less than 401 HP though because 401 Hp allows Jirachi to take 5 consecutive Seismic Tosses. Seems situational, but it's a small investment, so I might as well aim for it. I find that 404 HP and 257 SDef gives Jirachi the best chance it has at surviving LO Gengar's moves and allows it to barely survive inside of SR. I check to see the difference in damage I take from Salamence and Dugtrio, and I see that there is now a 0.07% chance of Jirachi not surviving Salamence. This is pretty much zero chance, so the final spread is 252 HP / 136 Def / 84 SDef / 36 Speed Impish.
Edit: Yay! Five stars!!!
Edit2: But five stars not from the troll! xp