Alright so with Skarner you have to and MUST KNOW when to go in and initiate ~
Most people think of skarner as a bad champ, and is useless *cough my friends cough* but if you play him right and know what your doing with your skills, you can prove to people that he is one of the most unique champs ever ;D

I get Tank runes because there very helpful early game, meaning that you can keep going in to a fight during low levels [1-4]

And again Tank Masteries because they will help you early game if you get ganked or going against some **** ad range.

start off with sapp to help you have enough mana to spam your Q early game. When you get Tears make sure to pick up boots.

I rush a Manamune because it gives Mana Regen+Mana+Attk helping you not run out of mana early game and late game. Also doing about 2-3 bars amount of damage everytime you use Q and a auto.

after that just get the rest of the items for Trinity force.

When you get trinity force get Atmogs for some extra AD but Tankyness for durability and a good amount of damage output

Exhaust

Flash

When your whole team is playing passive with the other team make sure your watching who is the closest person to your teammates then flash and ulti him and tell your team to get the person you ulti'd, when other people try to get you, run away unless you dont get focused then stay in there and help your team fight.

When you ulti a champion 1v1 use exhaust after the ulti breaks. If you KNOW you can take him out then go ahead and try to kill him. I choose flash to surpise enemies. Good luck~