Okay so viktor might be a touch underplayed/hipster champ, whatever his utility is undeniable and his ratios are solid (not the greatest, but solid).
this guide is a work in progress

His base move speed is quite decent.
His q allows him to be slightly closer to fights than some AP mids, however if you do not choose a good matchup in lane, trading with his q is not the smartest of plans
(ex. vlad: vlads q will heal him and damage you before your q comes back and provides a shield)

His W is his bread and butter, and this build is centered around it, especially early game.
uses for it:
Getting ganked? slap your w either in the path you are running or just on top of yourself, gives you time to just, walk away. and if you are good at predicting your enemies pathing during a gnak, just deny one and nuke the other one with q and walk away with a shield up.

You getting a gank? dont get cocky and just slam a field on the enemy champion, deny the easist path of retreat for them and creat a bigger opening for your jungler, this is a great way to snowball your lane as well as bait flashes.

other uses: team fight zoning, area denial when taking objectives ex:dragon baron blue, ganking other lanes, the range of it with the augment is gigantic, and its slow is dirty.

His e;
kind of leaves something to be desired, however it does put out some great damage as well as being a good farming tool. mana cost is a bit much but with the Field aug and utility masteries youll have a lot more mana regen which will help.

9/9/12
some people look at viktor and say why not 21/9/0 or more commonly 21/0/9 and to that i say, well moving faster, more mana/mana regen, more mr, and extended buff time leads to a lot more success in laning and lategame, not so much mid-game, since viktor is already dominate mid-game regardless of your mastery preferences.

the others are obviously viable, i do also like 9/0/21 for games where youll be doing a large amount farming.

Pros
great utility
good damage
great mobility
area denial
fantastic range

cons
has some pretty hard counters,
requires some getting used to
clunky casting animations
awkward early game.

the intro covers what they do and basic uses,
the rationale for my skills order is safety.
with w second you can deny early ganks as well as set up ganks for your jungle.

the rest is pretty generic, however if you notice at lvl 10 i get a second rank in w leaving you with q5/w2/e2/r1 i get the second rank of q at 10 because if anyone has gone merc treads the second rank helps greatly with landing those slow/stuns allowing for more (gaurenteed)damage.

everything else is just a given and requires little explanation other than the words do more damage

This is my build, Ive got somewhere in the realm of 30 wins with viktor with maybe 4-5 losses? mostly normal and a few wins in ranked with zero losses.
i go boots 3pot into a quick augment for gravity field. cause well, thats the entire point of viktor in my eyes. if you arent gonna use that, then go pick annie or some caster similar to viktor (annie came to mind cause of the similar skills (not range)).
this augment gives you great cdr, and great sustain in lane, not to mention the huge range on w which is, and i cannot stress this enough the best sh/t since sliced bread.

following this i like to go grab a kages, then farm a death cap. death cap is great damage, and without the death aug you need it to compete damage wise.

following this i make a dfg, its a great addition to your burst.
(tip: dfg travels alot faster than your q so if you cast it right after dfg will do its damage first) it also grants some more regen, decent ap and cdr.

i typically at this point assess the situation and decide whats best, between Void and abyssal, usually its void but abyssal should never not be considered. The magic pen from void is pretty huge and does a lot to make up for you only having 9 offensive mastery points.

follow up your decision with the one you did not choose. just because they do synergize well.

and cap it off with a Banshees, at this point aoe magic damage should trouble you much in fights, and well the spell block is great. sometimes i feel the need to get this right after my dfg, but more often positioning better can solve your problems

counters to viktor are champions with high mobility mostly in the form of blinks. due to the fact your e,w,r will be harder to land and but this build does provide decent mr so hopefully you can work around it, personally i just dont pick him against champions like Kat, ap ez, leblanc, kass, ahri, fizz.
but if you get counter picked, just lane swap when needed/if needed.
other things you could do is gank bot a lot, and have your jungle camp mid

Mostly damage with some sustain, and magic resist. pretty standard.

your roles in team fights range from pure damage to interruptions to zoning to denying an escape.

one at a time:

Pure damage,
throw down a w to protect the valued members of your team, you or the ad typically
do as much damage as possible, do not chase killing blows as your AD or bruiser/top lane is more than likely better suited to doing that. (this is assuming the fight has no clear winner)

Interruptions
toss death rays into the team-fight on primary targets while simultaneously placing your r and w on the enemy AP, which will not allow him/her to tunnel damage into your team, you need to use your range for this. DO NOT go streaking through the middle of a team-fight to achieve this

Zoning
Basically your r and w give you great tools for zoning, if you can prevent a player on the enemy team from entering a fight, while still being able to do damage with your e and q to the rest of their team, you should probably be doing that, (its very important to remember that while death ray is going off, you can cast other spells)

Preventing escapes
your w plain and simple can deny escape routes.
do that

comming soon