So this is my first build guide,
Varus is my main, but I have been playing him forever, thinking of getting Talon.
Feel free to comment any suggestions or make changes on your own!

EDIT: Got Talon, wrecked people's faces. I made this guide when I was pretty bad at this game, at least compared to now. I play this game quite a bit when I'm not at school, I don't have a job, or any income, so all of my 38 champs were bought with ip, I have gotten gifted 2 skins by my friends, (one for Talon [Dragonblade] and one for Varus [Archlight]).

So, Varus has a very low early attack speed, this makes getting cs and kills difficult, but not impossible. With this build it eliminates his main weakness, only to show the weakness of most all adcs, he's squishy.

Basically if you plan to adc, or play ad champs this is the most versatile rune page that I have come across.

21/9/0
Most commonly used adc mastery ratio.

In the Offense tree, we have Attack speed first (Important for Varus), then going down the line, AD, AD, AD, Armor & Magic Pen. (Varus benefits from both [W]), and more AD. Then we have +2 damage to minions, a tiny bit of sustain, +5% damage to enemies below 50% hp, and +5% of your max hp and mana when you kill someone.

In the Defense tree, we really just want to get to the +3% of max hp, you can play around with it if you wish, but I'd recommend just copying what I have.

The dorans blade start - I start with this 101% of the time with Varus, it gives sustain and ad, but will eventually be sold.

The other starts - These are just to get the ball rolling in the AD direction early.

First Back - When I play Varus I mainly focus on cs, and use my abilities sparingly (this may help with other champs), When I do use an ability (mostly Q) I aim to get at least 2 minions with it and hit the other adc or support. This said, getting extra gold for killing something helps, and it goes into the shiv.

Core - Attack speed, Varus has a pretty high early game damage, but lacks speed to make it work well, you need these.

Boots - Get basic boots after your avarice blade if possible, and bezerkers after shiv/pd.

Some Damages - I usually get BT then IE, but occasionally I'll get BOTRK then BT, then IE.

Really long game - In a really long game (50+ mins) your damage might fall off, IF and ONLY IF your damage falls of, you should trade the shiv for a phantom.

Situational -
Trinity - a lot of stuff in one item, AP may help that W out.
GA - Meh, I don't get it much, usually you don't live.
Frozen Mallet - You can kill someone who is running away easier, I recommend getting this if you're ahead.
Black Cleaver - some AD, Some CDR, some HP, and some ar pen. worth trying.
Maw of Malmortius - maybe if the enemy's Fizz/Ziggs/other ap/maybe Ez is kicking your but, you can try it.

My Usual is Flash and Barrier, can get away/chase and withstand a fight.

Optional Spells
Ignite - More Damage, but less ways to keep from dying,
Heal- Pop heal during a fight and live through it, not used widely anymore, you may get called a noob

I use Flash and Barrier, but that doesn't mean you have to also, I'm not the god of Varus, nobody is.

Q - One of Varus' great skillshots, get 'em low and snipe 'em dead, this also is great for ksing if you REALLY need kills. (please try not to ks though)

W - As you can see I max my W first, Why? because it gives you more basic attack damage so you can farm up and get CS and BUY YOUR ITEMS SOONER! This also works in with the masteries and adds about 30 ap damage to your hits at lvl 1

E - Also you may ask why I get my E at lvl 4 well that's simple if you kill minions easily you will lvl up faster, also kind of try to let their minions get to your turret so it's even easier farming. Slows all enemies who walk through, and has an on-hit mini ignite and damage. This is also Varus' escape mechanism, kinda sucks doesn't it.

R - Your ult, this baby has nice range, and snares the enemy then reaches out to snare other enemy champs nearby, if you land this, you have a much higher chance of getting those slippery enemies dead by your hand. I also use this in dire situations as an escape mechanism when the E won't stop them.

TL;DR R>W>Q>E

This stuff is OLD and outdated. And I'll have better proof soon.
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This will be a thank you Chapter but for now it is nothing, go out and play already!