Wee, Skarmory. One of the oldest support pokemon around (even if I don't see it being used very much anymore). It has an insane Defense stat, but mediocre everything else, including typing. One of the nice things about Skarmory tho is that it has a great support movepool, with access to Spikes, Stealth Rock, Roost, Whirlwind, and Sturdy to set everything up at least once. Overall, a nice pokemon for support, but that's really all it does. On to abilities, even though it only really has one good one.
Keen Eye: Easily one of the most useless abilities in the game, as not a single pokemon I can think of uses any Accuracy-lowering moves.
Sturdy: This is really what helps make Skarmory Skarmory. It allows it to set up at least one hazard, which is super helpful.
Weak Armor (DW): Lowers your Defense by one stage and raises Attack by one stage when hit by a physical attack. It would be helpful, but a) Skarmory has a pathetic physical movepool and b) by the time you've gotten enough of a boost to actually be helpful, you'll have such low health and Defense that you won't be able to do much.
It's a metal bird! No, not a plane, a Skarmory!
-Roost
-Stealth Rock
-Whirlwind
-Spikes/Drill Peck
Item: Leftovers
Ability: Sturdy
EVs and Nature: Impish (+Def, -Sp. Atk)
252 Hp/252 Def/4 Spd
This is a typical set for this airpla--excuse me--bird. Roost is to help sustain a bit longer, while Stealth Rock is, well, Stealth Rock. Whirlwind is to spread the love, and the last move is up to you, between Spikes for more hazards, or Drill Peck to prevent being Taunt bait and maybe finish off someone who's been damaged a ton by the hazards. You can replace SR with Spikes, but I personally prefer SR so that you will have hazards that hurt everyone for at least some damage. EVs and Nature for bulk, in case you need a physical wall.
Other Options
Brave Bird is what most people use over Drill Peck for the damage output, but I prefer Drill Peck as Brave Bird kills Sturdy, one of Skarmory's defining features.
Toxic and Protect can be put in to make Skarmory a staller...?
Countering Skarmory;227;
I mean, there's really not that much to counter. Unless you want to prevent it from setting hazards, in which case you want Espeon or Xatu for Magic Bounce. This really annoys Skarmory and essentially kills it. Meanwhile, Taunt is also frustrating, especially if it isn't running Drill Peck/Brave Bird. If you want to kill it, just keep hitting it with SE moves until it dies, but make sure to have a spinner, as it will set up on you while you try to kill it.