As a Viktor main, (around 130k mp on him atm), I have a few tips you could use. In terms of positioning in teamfights, viktor has somewhat short ranged compared to a velkoz, varus, xerath, and so on and so forth, he doesnt have too much mobility aswell aside from his movement speed boosts. Before a teamfight try to poke using your laser, and when you think you can clean up or if the enemy isn't focusing you, try to unload your combo on as many people as you can (prioritizing the enemy carries.) Late game your laser should do around half health of the enemys ADC, so if you can chunk them before a fight starts, it will be much easier to kill them. In terms of laning, early game viktor is a strong bully, especially to melees, try to use your Q for the shield and auto attack damage to poke, and follow up with a laser. Something that works with laning and increasing cs is buying a second dorans ring after getting your first E augment. The double dorans gives enough sustain to allow you to freely try to clear the whole enemy minion wave using one laser and a few autoattacks. The nerfs didn't hurt Viktor too much, he's still really strong, but just weaker early. During lane you should also try to poke the enemy along with clearing the wave with your laser and Q, and if they have around 50 - 75% health you can all in them with a full combo + ignite. Sometimes ignite isnt the best choice for Viktor, as he's weak against assassins and enemies with high mobility, thats why you can also get things like ghost, barrier, heal. But always try to remember, Viktor is short ranged, it's easy for him to get focused in a teamfight if the enemy can survive your burst, I love viktor and I started playing him before he got popular in the LCS and now in solo queue, keep playing him and the more you master him the better you can do in game.
EDIT: Keep in mind I am in Gold right now, nothing too high but I main Viktor so, that's only what I can really say.
