Hello and welcome to my Jungle Skarner guide!
I play Skarner in ranked as a hybrid jungle carry, and I want to tell you how, and why this works for me. And hopefully it will bring my fellow Skarner players some good fortune!

Pros:
1.Amazing Ganks if done right.
2.Able to do decent damage and take a lot of damage with his shield early on.
3.Very mobile

Cons:
1.Fairly squishy, needs to have defensive items
2.Very susceptible to CC
3.No real gap closer or escape mechanism (I guess MS from W IS a gap closer though...)
3.Counter jungled easily, and not great at counter jungling.

I feel these runes work very well for Skarner.
The attack speed works well with his passive, more attack speed means more spamable abilities.
The armor seals are a no brainer.
And finally, the movement speed quints work well with Skarners ult. I will explain later.

These masteries work very well with what I use Skarner for. 1/14/15 to grab the cd and extra gold for Smite, 14 in the defensive tree to make me a little tougher, help with regeneration, and give me a bit more health. Then I put 15 into Utility mainly for the movement speed, which once again helps with Skarners ult.

My starter items are basic Jungler items.
Wriggles is an amazing item, period. I choose berserker greaves for the AS. It is very valuable on Skarner. Next is Sheen, and I feel that Skarner was designed to use this item. He has such a spamable skill set that it would be rediculous not to buy this. Finish building trinity force, this item is PERFECT for Skarner, move speed, another slow, and that wonderful proc. Depending on how well you're doing here is where you can branch off, it is just very important that you finish trinity nomatter what. Here is where you decide if you get the Hextech Gunblade and continue stomping face, or get a Banshees or GA to save your scorpion A**. Essentially you should fill up with whichever items you did not pick, GA, HexTech, or Banshees.

You are probably wondering why I max out Skarners shield instead of one of his damage spells. It's very simple, survivability, movement speed, and attack speed, allowing you to spam your 1 point in Q to keep them slowed, and keep procing Sheen. I will explain why this is so important later on. I don't really have a preference on leveling Q or E first, as long as W gets maxed out, if you feel you need the heal off E then max it. If you're raping face, and want to keep them even slower than usual, max out Q. The decision is yours.

I start at the blue golem when I jungle with Skarner, starting with Q. I press my team to give me a leash at blue, it isn't completely needed, but the faster you can get blue down the better. I have had leashes where I didn't even need to use a health potion after Blue. To increase your chances be vocal, and ask whichever lanes are the closest, to both do damage to the golem after it is leashed. Afterwards, I go Wolves > W > Wraiths > W > Red > Small Golems > E, and depending on how bottom lane is doing, and if you got a decent leash at blue, you should be around 3/4ths maybe even 4/5ths HP, with about 1/4th your mana, but that wont be a problem since you have blue buff, you should be able to get an easy gank.

Skarner is not a champ that you want to be super aggressive with without having help from the team. While he is capable of good ganks, if your team is overextending, or unwilling to commit to a gank, Skarner really isn't a champ that is going to be able to pull a golden egg out of his A**. You need to be very verbal with your team and tell them when you're planning on ganking, try to make them get into position when you get there, because if **** goes south before you can catch up to the enemy, it's gg. I know the same goes for any gank scenario, but I look at Skarner like another Udyr, You have to physically run to the enemy, you aren't amumu, you can't bandage toss, you can't fly to them from half way across the map, you can't alpha strike to them, or charge at them, you have to run to them. Your team needs to realize that the gank isn't going to go well if they are back behind their creeps, and start running away when you run in. Even if you land your ulti and drag them back, how your team reacts is going to decide if the other person gets away or not.

I love using Skarner in ranked play! You almost never see him, and that honestly gives him a handicap. No one knows how to play against him. You get a bunch of Bandwagon players thinking he sucks just because he's not op in any way, and everyone else says he sucks.

So I start out my jungle at blue, I like to ask at least one person to watch wraiths for me, and have everyone else defend blue incase of ganks. I really push for a good leash on blue, the faster you get blue buff the better! Skarner is SO mana dependant, but with an infinite supply of mana, he is unstoppable! I don't try and counter jungle, if my wraiths are gone, then oh well, i go to golems, get level 3, and finish red then try to gank either mid or bottom. Vocalize with your team, tell them this is what is going to happen, after red buff they will get a gank. If it was successful, great, if not, oh well, dust off, recall, and head back into the jungle. I try and gank whenever my jungle is clear, which should be always, if you aren't ganking, get in the jungle, clear minions out as fast and mana efficiently as possible, then start ganking again!

After your first trip back, you should have enough gold to get madreds! Some people buy boots their first trip back because it helps with ganks, well the wonderful thing about this build is you don't need boots! Your MS Quints and Masteries coupled up with your W are all the "Boots" you need! With madreds life becomes good. You can go through the jungle much easier, without using nearly as much mana, keeping you able to gank whenever is needed.

I constantly talk with my team when I play Skarner, his strong point is early/mid game. If you don't get some kills, or at least secure kills for your team, then you are going to be useless late game. Skarner NEEDS a lot of early farm, you gotta keep some mana and health pots on you at all times, and you gotta keep that W up, burning through the jungle, keeping it clear so you can get back out and gank for your team!

The typical gank for me goes like this, I'll finish my jungle route, and instantly look at the closest enemy to see their HP, even if they are full HP, if they are pushing really hard, I will go for a gank. But if they are full and playing safe, then I search for a new target. I'll tell the lane im heading there to gank before I even get close, just so they can prepare for it, and hopfully let the enemy push a bit. Then by the time I get there, even if they have it warded, I can W/Ghost and run up, Ulti, Q, drag them back as far as possible, away from bushes, and their turret, hit em with another Q right as the stun ends, to proc the slow, and by then your W should be just about up again, hit W, keep Q on em, and launch an E if needed, in most cases your auto attack will do more damage, but if you need it to last hit, or to proc sheen, then go for it.

Late game you're going to be a sniper. There are two things you can do. One, you need to get onto the squishiest carry they have as fast as possible, and even if you sacrifice yourself, you need to drag that person to your team and let them get a kill. By then you've probably exhausted most of the other teams skills and spells, and eliminated their carry, while keeping yours alive. Whether you live or die, their carry is down, and their team SHOULD be taking some crazy damage by now, and not really able to put out enough to keep up. Or two, you can wait for the fight to start, blow W/Ghost, run in and grab the carry, pull him wherever is safe, and burst him down. Which if you have trinity/gunblade, is completely possible. Skarner doesn't have great survivability, and in late game, you basically need to do the most useful thing, which is keeping THEIR damage out of the fight. Yes you can do a decent amount, not as much as a carry, and you can take a decent amount of damage because of your W, but if you get focused you will die. So I suggest playing more of an assasin role late game, with a huge risk/reward thing going.