Skarner is a hybrid Melee, Fighter, Jungler; adept at crowd control, area of effect damage, and ganking.
Ability Details/Skill Sequence
Skarner's passive is Energize. Each of Skarner's basic attacks reduces the cool-down of all of his abilities by one second. The cool-down reduction is greater against enemy champions.
Skarner's first ability is Crystal Slash. Skarner lashes out, dealing area of effect magic damage in a small radius. If Skarner hits an enemy, he becomes energized and his next Crystal Slash will slow each enemy hit. I take Crystal Slash at level 1 and max it immediately.
Skarner's second ability is Crystalline Exoskeleton. Skarner encases himself in a crystal shell, gaining a shield as well as a movement speed and attack speed buff for a short time. If the shield breaks or the ability times out, the speed buffs end. To get the best speed and shield out of Crystalline Exoskeleton, I take a point at level 3 but max it by level 13.
Skarner's third ability is Fracture. Skarner sends out a wave, dealing magic damage in a line and marking all enemies hit. Receiving damage from Skarner through attacks, abilities, or masteries consumes the mark, healing Skarner. The first mark consumed heals for the greatest amount while each subsequent consumption heals for a reduced amount down to a cap. I take Fracture at level 2 but max it last.
Skarner's ultimate is Impale. Skarner encases his target in crystal, dealing magic damage initially, suppressing them for a short time, then dealing additional damage when the effect ends. During this time, Skarner can move his target around the battlefield. Although he can't activate Fracture or perform basic attacks, he CAN activate Crystal Slash, to prepare a slow for his victim, and his Crystalline Exoskeleton, allowing him to drag his opponent even further.
For runes, take flat Attack Damage Marks, flat Armor Seals, Magic Resist per Level Glyphs, and flat Movement Speed Quintessences.
My masteries are 20/1/9; taking all the Armor and Magic Penetration in offense, improved Smite in Defense, and Mana per Level, improved Recall, Movement Speed, and improved Neutral Buff duration in utility.
For summoner spells, I recommend Smite and Ghost. Flash is also effective, but doesn't aid in chasing down enemies.
Creeping / Jungling
Start at the Ancient Golem buff and have your teammates guard you from enemy counter-jungling and leash the Golem when it spawns for some free damage. Failing the pull, Skarner is capable of soloing the Golem while only using two Health Potions. Be very careful of enemy Junglers like Shaco or Nocturne who specialize in letting you do all the work then stealing the buff with Smite. If you see the enemy team try to gank you at blue, don't fight, run to the other Golem camp in the opposite jungle.
Once you've gotten the Golem, head for the Wolves, then look for ganks in the appropriate lane. Mid-Top from blue team's jungle, or Mid-Bot from purple team's. With Ghost you can surprise your opponents with an early gank and possibly pick up a kill/first blood.
If no ganks are readily available move to one of the two Wraith camps, then the Elder Lizard, look for ganks once you get Red buff, if a gank is available, skip the small Golems. If not, take the Golems and recall/repeat.
>> Blue Golem
>> Elder Lizard
>> Gank/Small Golems