To simply put it, your early game is going to be annoying as can be. Just focus on landing your E on the enemy ADC and grabbing Siege minions to get really tanky really early. Always remember to secure your spires around the map when you decide to roam and be sure to get some deep wards in the enemy jungle to help out. Low on mana? Go to a spire. Need a quick get away? Make sure the River spire is secured and you can make a speedy getaway to Mid lane.

This is where things get spicy! ^^
Your mid game power is ridiculous. By this stage of the game you can tank towers for kills and live. Your most basic combo will be to dive the enemy ADC when they are low, W for the shield and Ult them, drag them from under their tower, and BOOM Randuin's. This is the most annoying thing you can do to an enemy and often tilts them. Now when it come to team fights, forcing fights in the jungle is always a good idea because... well... Skarner spires. While team fighting, you'll have to pick and choose how to use your ult and who to use it on. Wanna be aggressive, W dive the biggest enemy threat and Randuin's the entire team. Wanna be defensive, W dive and drag the hardest one to kill behind the enemy team. They'll be so busy trying to get their best fighter away from you that they won't realize the rest of your team shredding them to ribbns. However your ultimate isn't your only tool. Your ult drags people but, your E completely shuts someone down and it doubles as a slow. E, Randuin's and AA, easy kill.

Do you like crystals?
Do you like unfair jungle fights?
Do you like diving turrets?
And do you like being the one thing more annoying than a fed Teemo?
Then Skarner, the crystal **** is for you!
Literally late game, you are the most annoying thing possible. You're ult is up practically every 40 or so seconds, you eat damage like it's nothing, and you can LITERALLY tank forever. You are your team's front-liner and you hit like a freight train. You can single out enemies and pull them out of position while barely getting hurt. Skarner may not be a META support but, he brings damage, utility, and especially joy to his team.