Max q and w first while getting a point in e at level 4. Your q and w supplement each other extremely well while giving you more survivability through your shield. Although the heal from your e is helpful it is not worth the mana costs as Skarner struggles with mana early to mid game if you don't buy any mana regen.

The dorans ring gives you extra health as well as mana regen which is crucial to being able to spam your abilities. Rageblade is your most important item. It gives you both ad and ap while also giving u attack speed. It allows u to spam your q to keep up your rageblade stacks while also activating ur passive to cool down ur abilities. Next you get lich bane so that between q's your auto attacks hit a lot harder. Rabadon's adds to your auto attack damage thanks to your lich bane while also making your other abilities better. The Hextech Gunblade gives you more survivability through life steal and spell vamp as well as giving your q both ap and ad to hit harder. Finally the Rylai's gives you extra health while allowing u to slow them with your e i they get out of range with your q slow.

Skarner is a ap mage however he doesn't need the survivability given through the defensive masteries as long as you buy a dorans ring to start. If you prefer you can put some of your points in Utility into defense to give u even more early game survivability.

The extra Magic pen allow you to buy beserker greaves without sacrificing too much of your magic damage while the armor and magic resist give you more early game survivability as you are a melee character.

I like teleport and flash because i feel that one summoner spell should always be dedicated to escape and I prefer teleport because it gives me the best map mobility but that is just a preference.

Skarners ult is a very useful ability when protecting a tower. To ensure its best use be sure to allow the enemy champion to attack you and aggro the turret. Also to maximize your damage remember you can use your abilities while you have ulted which allows you to use ur w to drag them farther and ur q and e to do more damage while they are suppressed.

I hope this build has helped you. Please leave comments so that I can better improve my guide.