Let me get this straight first. I ain't no Dimond player (Ain't nobody got time for that); I'm a player who gets stuck in silver and not that good. Also, I'm Asian with bad English, so if you experience grammar mistakes, just ignore it b/c I'm way too lazy to check it over.
Anyways, it depends all on you if you want to follow this guide.

I'M NOT TAKING RESPONSIBILTY IF YOU LOSE THE RANK GANE OR BO3. :P
SORRY ABOUT THAT.

Pros:
>Super good long range poke (and it hurts like hell)
>Good cc
>The shield gives trading ability
>AOE silence
>Good early game AP (Because of your passive)

Cons:
>Not tanky
>Short casting area
>High mana cost
>No escape
>1 less item slot b/c of the passive

So yeah, the passive if God like early game, and it's like **** late game.

As a top Viktor, winning early game to snowball is necessary.
Since that you have good poke, you shall be fine doing so.
For the item, get flask and some blue pots to ensure the continuous poking since you have a high mana cost.
First back, you can get catalyst to have a good mana and health regeneration to stay in lane for a long time. Later, get the Augment: Death to farm and poke better. Also, just get boots before ROA.
During the middle game, try to finish ROA asap to get the health and dmg. If you are getting focused, get Zhonya first then death cap. After the death cap and Zhonya are done, get Rylai's Crystal Secpter to get dem slow.
At the end game, sell your boots(since you should fight like a man without backing up) and get a void staff. By then, you can walk in like a boss, drop your w, use your e, call out your ult, and Zhonya and get a penta. (Use q after Zhonya to get the shield for surviving)

ALWAYS MAX E FIRST.
E gives you the long rang poke and the high damage.
If you are getting zoned out, use your e to harass the enemy while farming.
Max Q second for the shield.
The reason why not to max Q first is because of the lack of damage and the thin shield.
That shield doesn't do that much compare to your E.
Get ult when ever it is possible.

In top lane, try to poke while farming and keep a ward in the bush by river.
If your enemy jump or engage on you close range, q him, drop the w, and e.
After that, use your ult and ignite if you want to.
However, if your enemy is like Akali or any other mage, drop ult to slience them and watch them suffer.

In team fight, let your team initiate first. After the fight breaks out, try to use w to catch max amount of people and drop your ult and use the e. If someone runs to you, use q to shield. After you drop your ult, try to keep up with it so that it will move faster. (If you have a Rylai's Crystal Secpter, they will be slowed to death no problem)

While your team get's caught, just put down your w in the escape route and use E and Q to do as much damage as possible. Also, when your team catches someone with cc, use your w on them to keep the cc chain going.
TBH, you don't really have a lot of disengage abilities.
(Why I don't usually use my ult to disengage is because it is too important to lose)

I'm lazy. I'll finish this part later.