Don't pick him. But if you really wanna swag it on the battlefield you can use this guide.

Okay lets start of with telling you, this is a "HIGH ELO GUIDE" so like if you are Bronze,silver,gold,plat5-4, you can't use this guide since it only for high ELO.

Starting items: Elixir of Fortitude 3x Mana Potion

Core items: Rabadon's Deathcap Trinity Force Sorcerer's Shoes

Late game items: Rabadon's Deathcap Trinity Force Sorcerer's Shoes Rylai's Crystal Scepter Hextech Gunblade Twin Shadows.

So before you go to lane you wanna start with Elixir of Fortitudeand 3x Mana Potion. The reason for these items are, that you'll get health from Elixir of Fortitude, because of that you can run full Mana Potion so you'll be able to push your lane to the turrent and start giving dmg to the turret.

If you die ( you probably will if you try this at lower elo), then check if you have enough gold for Needlessly Large Rod and if you can't afford it then go back straight to lane without getting any wards or potions since it will only slow you down in getting your high dmg.

When you finally get your Needlessly Large Rod around 10min mark ( since you have killed the enemy serial times). you will be able to keep push with the motto "It's fast it's fun it's domi ups Viktor.

You will probably end the game around 20min mark because of your high pushing potential, you can follow my item build to see what you should build after Needlessly Large Rod.

Reasoning behind these runes are:
You really wanna scale into late, because that's were you will be able to show off the most amount of swag and disrespect, which is really important in winning games as Viktor.
This has the same principles as a ADC sorry Marksmen, you really wanna get that lucky crit in lane while you're auto attack trading with the enemy.
And again you don't wanna fall behind so you wanna run scaling AP runes, since early presence will be done through your Yellows.
Okay we all know that experience is important so you wanna run these so you will always be at the same level as your enemy or even ahead.

With this guide (IF YOU'RE HIGH ELO) you will win any matchups, so nothing to explain about it.