General
You are the ADC (marksman as riot like to call it) of the team. You are squishy and deal a lot of damage. Early game you will get carried by supports (that's what they do).

This is my first guide so i hope you find it useful

Pros:
-His passive is really good in team fights
-Long range poke to Singe a turret or defend one
-His ultimate to lock down teams
-His Auto Attack Range is 575 which is higher than most ADC's

Cons:
-Varus doesn't have any escapes and you need to rely on flash and your good positioning to stay alive and out of danger.
-A bit mana hungry

Ideal supports:
Nami - CC, Heals and disengage
Janna - CC and disengage
Leona - CC and Tank
Thresh - CC,Tank and lantern escape

Summoners

Barrier or Cleanse?
-Barrier is really good for trades in lane and burst champions
-Cleanse is really strong for escaping, chasing and doing damage

Flash is a must as he has no escapes.

Items
-Doran's Blade is now cheaper. It lost some stats but is still a good choice to buy.

-I prefer BT in most circumstances, however if they have a tanky team and/or have a tank snowballing hard then i suggest Blade of the Ruined King.

-I tend to take at least one tanky item but that's your choice.
-When i reach 6 items i sell boots and get zephyr. It give tenacity which is awesome!

Runes
-I went for standard defense runes and AD marks for last hitting.
-I went 6% life steal as they have changed minion HP and Turrets AD so you can last hit easier which means you can trade and stay alive

-I have taken a very offensive heavy Mastery setup. I have been messing around with the Masteries and think this is the best way to go.

-You could chose to put points into "Spell Weaving" and "Blade Weaving". i have chosen to go with Expose Weakness (When you hit an ability allied champions do more damage to the target) because if you hit your ult your team will be doing a little bit more damage. The defense tree isn't worth putting 9 points into so that's why i haven't gone far into it.

Abilities
-His E got nerfed pretty hard a while ago. I tend to max Q now then W. E is used to pop the blight stacks and Q is used to Harass from far.
-Blight also helps with last hitting so you don't lose so many :D

Laning
When the enemy ADC goes to farm AA once or twice then use E to pop the blight stacks. Try to poke down with your Q all the time but keep an eye on your mana. Varus can go all in and with if he has a good amount of mana.

Team fights
Stay at the back and do damage to the closest target (blight does % HP damage)
You can use your ult to lock down the enemy at the start or mid team fight. It is a good pick off tool and don't be afraid to use it.
Be patient and don't go too deep, you aren't Ezreal and can't shift away

Varus is a very versatile champion with many different builds.
He has a lot of damage and peel but needs to be protected
Good poke
Scales well into late game
Good farmer
Good team fighter