Pros:
+ The master of chasing down enemies
+ Shredding with his Q+E (with rylais exceptionally well)
+ Strong counterjungler!
+ Pulling deliciously squishy targets to your Team (nom nom nom)
+ HE IS AWESUM

Cons:
- Must get close in Melee range
- When you don't have a tank you are screwed
- Need to position yourself good

The old Skarner came into the fight by engaging with his W, Q'ing while slowing targets.
Nowadays the Q doesn't slow anymore and the Q cd is higher.
So we put the cd lower by abusing the Devourer enchantment.
Every second attack (whilst devourer is full stacked) makes the Q cdr effect for attacking act as it would attack twice at one time.

In the lategame you have to upgrade your trinket (warding totem) to achieve some vision on their jungle.
Killing them in their own jungle, by taking them one by one is one strategy.
You can also go for the "Righteous Glory"-Item which boosts your Movementspeed heavily by moving towards enemy champions, this effect is so good for taking down the focus.

Thanks for reading my first Guide on how to eventually try out Skarner,
I have to say, english is not my native language so don't be critical :D
I hope you enjoyed testing it out soon ^_^