This is my aggressive play AD focus Varus. Below I'll include strategy explanations for my choices on items and skill sequence but the runes and masteries are both of the same, basic mindset: to create a terrifying predator. (The only funny thing is the single point in Expanded Mind. This helps maximize utility efficiency.) Follow the guidelines listed bellow and you can walk out of a match with a +20/0 KDR.

Build The Bloodthirster, max the stacks, kick some ***!

In the Beginning

Start the match with a good ol' Doran's Blade. You could start with Boots of Speed and a couple health potions but they do not give you the beginning game survive-ability that Doran's Blade does. Besides, after your first level or two you should have a kill under your belt and can Recall and pick up your very own pair of Boots.

Vital Items!

With Doran's Blade and Boots of Speed, play it sneaky. More or less, steel kills and save for the B. F. Sword. You can promptly pick up the Vampiric Scepter or just wait for the cash to get The Bloodthirster.
The Bloodthirster's life steel keeps you alive in a fire fight. It allows you to get your hands dirtier and keeps you alive so you can get those last hit kills.

And the rest...

Berserker's Greeves help put out damage fast and get the minion kills to max The Bloodthirster.
Now, the reason we build Stinger into Nashor's Tooth instead of Phantom Dancer is the cool down reduction. Most of the time you will find yourself waiting on the excruciating cool down of both the Piercing Arrow and Hail of Arrows. The Phantom Dancer can be built but you'll still be waiting that extra few seconds on your skills to cool down in combat.
The Black Cleaver, Phantom Dancer and Nashor's Tooth are all late game, interchangable items. All of them get the job done. Finishing up Nashor's Tooth will be easy to finish but The Black Cleaver gives you the firepower to clean up the battlefield and sabotage those high power tanks late game.
All-in-all, The Bloodthirster, The Black Cleaver, and the Infinity Edge are the basics for a powerful AD.

Just like the Bloodshirster: Max the stacks, kick some ***!

Blight and Fight

Max Blighted Quiver a.s.a.p. It gives you, at first level, that extra bit of juice needed to cripple your opponent and get those last hits for minions.
At 2nd level, you won't be able to choose Blighted Quiver, but you won't want to. Choose Piercing Arrow, clean up the minions, and chase your opponents. When they are just out of your basic attack range, finish them off with W. Time the double cast and let it max out. Don't be afraid to step inside that turret, just don't stand there.
ABOVE ALL THINGZ! Let the blight stack. When the blight explodes, it deals percentage damage, not a base damage. That puts Tanks on their ***es.

Utility

Hail of Arrows, E, and Chain of Corruption, Ulti, are Utility abilities so put points in them early but don't max until late in game. Practice using Hail of Arrows to slow down fleeing opponents or slow down a raging tank.
And, as far as I'm concerned, Chain of Corruption is virtually useless in any kind of pinch situation. It spreads too slow and immobilizes instead of stuns, so an opponent can still destroy you while wrapped in blight.
While all these things are awful about Chain of Corruption, it proves helpful in a mass champion assault or running solo TOP/BOT. On more than one occasion I've held my ground, picked up kills, and taken down turrets running solo. Often, opponents will try to double and triple team a solo player because they obviously have the advantage. Chain of Corruption evens out the fight late game. You can do enough damage in the 2 seconds it gives you to put down one champ and handle the other.

But, if you ever find yourself in a pinch, Hail of Arrows will get you out as fast or faster.

Don't be afraid to steel the kills

Laneing

Most people will tell you that a champ can only do so well based on the lane they chose. With Varus, it's about the fighters and tanks. If you lane with a melee fighter that can't follow through then you capitalize. It doesn't matter whether they float BOT or TOP, your opponent will run and you will snipe there faces off.
Tanks will be the best companions because they don't dish out the damage fighters do, and offer a great sponge to soak up all that minion and champ damage. This gives you a good shot at the last kill and walking away with most or our life intact.

Solo

This is out of the question early game, but once you've got The Bloodthirster built, Level 6-10, you can play a safe solo lane. Hug the turret and keep your distance. Like I said in Items, The Bloodthirster will keep you alive and give you the firepower to really put a dent in oncoming champs. And don't forget to utilize your utilities (E & R).