I already played Viktor 600 times, so i really know what the best build on him is. A few things about me: I am a Bronze V main mid laner. I play 23 hours per day but only against bots and one hour against normal people. Now you can imagine that my skill is incredible high but I only get feeders on my team, thats why I am stuck in Bronze V.

ALWAYS, i repeat ALWAYS use ur ult for the jungle camps, it saves a lot of time and your jungler doesnt need it anyways.
Early Game: Try to make last hits. I usually have a cs of 10-20 in 10 minutes.
Mid Game: Try to push your lane, so you can roam a lot with your high mobility. This is the moment when your damage spike begins, so don´t fear a tower dive. (just try to ks as much as you can.)
Late Game: If you already finished your sunfires you can act as a bruiser and be the front line, you are the iniator of the team now. With your insane dps you can 1v1 everyone (NOT NASUS, his slow is a carrot).

Pros:

Hybrid
Mid game Power Spike
High attack speed with lifesteal
40% Cooldown reduction
High mobility
Really strong with high cc
Late game strong frontline
Easy to learn, easy to master

Cons:

Your damage in late game sucks rapidly
Bad against high cc
Really, really, really, really bad in LvL 1 trades

Passive:
This is the real 20cm and you can improve your Rod and get a huge power boost.

His Q spell:
U shoot a triangle circle to your enemy and get from his life a armor forged from his skin that you ripped of. As a bonus you get a monster AA like lichbane but more like BAAAM in your... . If you improve your Q so you get a nice movement speed.



His W spell:
A little gravity ball that slows the enemy, but if the enemys stay longer in it, it stuns. If you Improve your W spell you get a cuddle sweet little orianna ult and this is sick man.



His E spell:
A high damage Skillshot Lazer with high damage. Its a bit tricky to figure out how this lazor works but if u can handle it its a great spell with high damage.
If you improve this spell you get more high damge to your high damage.



His Ultimate: A strong AOE storm that chase your enemys to the nexus tower.