There are 6 summoner spells that Viktor can take but most of the time I take Teleport and Flash. Ofcourse you take Flash since you don't have any other kind of dash or ability to get out of a bad situation. I think Teleport is a very good summoner spell to never get behind and be somewhere to turn the fight, it also makes you able to splitpush because you can waveclear fast. That's why I take it almost everytime. If you die to gank you can simply teleport back in lane and you won't miss any experience or gold. Ghost is a good summoner spell on Viktor. It gives you a lot more kite potential and the ability to chase someone while keeping your Chaos Storm on them. It's also great if you are planning to roam to another lane or get to fights faster, but it's also good for running away from ganks. Together with your augment upgraded Siphon Power you will outrun almost everything. The only reason you might want to take Cleanse is if you are facing an enemy/laner with cc, like Twisted Fate or Veigar (and possibly if the enemy team has too much cc). It will also let you get out of sticky situations or ganks if you ever get stunned or slowed. If you are up against an AD laner or assassin then I would recommend taking Exhaust. A good example is a Zed, Talon or Yasuo matchup. It's a very good summoner spell that most of the time will save your life or help you kill someone. Barrier is very useful against champions with high burst damage. I only ever consider taking it against Syndra or LeBlanc as it most of the time saves your life and helps you greatly in lane. Also, it guarantees you surviving most ganks. I rarely see people taking Ignite on Viktor but it's not very bad. It gives you a lot more kill pressure as Viktor is known for his lane pressure and poke. You probably won't be taking this unless you really want to kill your mid lane opponent. As the game goes on, Ignite becomes more irrelevant and most of the time you will find yourself in a situation where it could have been more useful if you took another summoner spell.

Keystone

Summon Aery: Very easy to proc off and because you can poke a lot.

First rune

Manaflow Band: Good rune since Viktor does have mana problems

Second rune

Transcendence: Extra 10% CDR, very good because with blue buff you will have 45% CDR and with that you can have an constant Q shield up. You can even solo dragon because of that since you don't lose hp.

Third rune

Gathering Storm: As I said the goal of this build is to scale hard into mid/late game and what better rune is there than Gathering Storm.

First rune

Minion Dematerializer: So you can push wave faster and get those chunky cannon minions out of the way. Always use one of it on every type of minion and the rest of it on cannon minions to push wave if enemy mid laner tries to roam or recall.

Second rune

Cosmic Insight: Extra CDR is always handy. This together with CDR boots is great on those long cooldowns on Flash and Teleport.

This is most of the time the first item I finish before anything else (except boots). The upgraded skills are necessary for wave clear and the movement speed is also very handy for better kiting.

The boots I always go for normally. The extra 10% CDR is needed to get to 45% CDR and it also lowers those long cooldowns on Teleport and Flash. Above all it's also cheaper than most boots.

Not recommended to buy because you rather want Ionian Boots of Lucidity to get to 45% CDR for a permanent Q shield and just overall lower cooldowns. If you rather want the magic pen then go for it, I'm not stopping you.

If the enemy team mostly consists of assassins or AD then you should buy this. You should also buy this if you are laning against a AD champion like Yasuo or Zed.

Buy this if you are facing an enemy team that has mostly AP damage or if you are having trouble facing a strong AP mid laner with cc.

Viktor is known for his strong trading potential and lane pressure.

On level 1 you want to start with Siphon Power and use it whenever you can to proc Summon Aery on your opponent. Simply using Siphon Power with/without an autoattack is good enough to put pressure on your opponent without taking much damage yourself especially if you are up against melee champions.

After that you want to focus on making your opponent lose farm and poking him if he comes too close. If he goes for the last hit on a minion you can poke him with Siphon Power and Death Ray. This ensures that your opponent will have to choose between getting farm and getting poked or trading back and losing farm. Whereas the most case is your opponent going for farm and getting poked.
If he get's too low then you can simply kill him with Q + AA and E. Don't be afraid to use Flash if necessary to kill him.

Viktor is pretty mana hungry so do not use your Death Ray too much just for a simple poke if you are almost low on mana.

If you successfully gained lane dominance or an advantage you can pressure him by just walking towards him. He will walk back because he doesn't want to get poked. If he does so he will lose farm and maybe even experience if he's too far away from the creeps. Pressure isn't all about winning trades but also making your opponent afraid to come close to get farm.

Now you don't want to get too close or getting in extended fights. If you get too close you risk getting to die since you don't have the potential to kill someone quickly before they kill you. Keep good attention to the distance between you and him.
Do not prolong a trade after you used your abilities. If you do then you will most likely end up losing the trade making you the one with lower hp. It's never good to already be low on health in the early game as Viktor since it makes it harder for you to stay long enough to earn enough money for items.
Simply use your Death Ray + Siphon Power and if possible an extra AA and walk away. Most of the time that's all you gotta do to win the trade since you can almost instantly cast it.

Viktor also has extremely good waveclear. Once you get augment upgrade on your Death Ray you can clear the whole wave. Now you simply want to push the lane 24/7 so your opponent has to farm under turret and lose cs or facetank the entire wave.
Not only does this give you a lead, it also makes sure your opponent won't go anywhere. He will have to stick around his tower if he want's to get his cs and if he doesn't and decides to roam he will lose farm while you are damaging his tower. If he doesn't get anything out of the roam he will only be put at an even bigger disadvantage.

This is also where Minion Dematerializer comes in handy if you have it. It's great to push a cannon wave fast.