This guide is not complete I will be updating it soon.
If there is something you would like me to add please let me know in the coments section.

This is a guide to an AD Varus.
Try to get the mid lane when ever you can.
This is a guide for all players and works for all types of lol games
Remember this guide is not perfect so dont be fraid to try something different then what i have here and if it works better then perhaps you can share it with the rest of us in the coments.

Pros

Fun to play
Long range
Good at harrasing
ult can hit all oponents in team fights
great ad carry if played right

Cons

Long cooldowns
Squishy
Gets targetted a lot because he is the ad carry

Greater Mark of DesolationGreater Mark of Desolation:

I get this because Varus does a lot of ad damage. If the oponent(tank) was to get a lot of armor then Varus would be doing little damage to him and he could perhaps even kill you or last long enough for backup. This runes can help you penetrate through some of that armor.

Greater Seal of ReplenishmentGreater Seal of Replenishment:

I get this because Varus runs out of mana too quick. I harras a lot using my pierce of arrow right from the start and farm a lot using hail of arrow once i reach lvl 6 so he runs out of mana before you know it.

Greater Glyph of Alacrity:

A little extra attack speed is always usefull specailly for ad ranged characters. It lets you take down melle oponents before they get close enough to attack you.

Greater Quintessence of Strength:

I get this because the bonous attack damage early game can give you the advantage you need to win your lane.

You are the ad carry so you must farm as much as possible.

Hail of Arrows is a great ability to farm with but it takes a lot of mana so dont over use it especially early game.

Recomended:
I use this mainly for escaping and sometimes for escaping.

Lets you stay in lane longer to farm and take down enemies when you have low health. It also helps you take down enemies who are a little stronger then you.

Usable:
Use it to take down enemies with low health who are about to run behind there turrets.

Use it to runaway, chase,or get to a different lane faster to defend.

Use it to get to a turret underattack or a teammate in trouble fast.

Use it to chase down and make an enemy easier to kill.

These items are not set in stone so dont be afrid to make some changes depending on the situation

Situations:

Fed enemy champion like Tryndamere that does a lot of ad damage you might wana buy a
Thornmail

Piercing Arrow

Use this to harras and kill enemies from far.
This can help you stop enemy from farming.

Blighted Quiver

Lets you do bonous damage.

Hail of Arrows

Use this ability to farm
Use this to help your teammate get away from a enemy that is chasing them.
Use this to get away from an enemy that is chasing you or slow down an enemy that is trying to run away.

Chain of Corruption

Use this ability in team fights to deal damgae and imobolize all enemies. This can give your team the advantage they need to win
Use this to help your teammate get away from a enemy that is chasing them.
Use this to get away from an enemy that is chasing you or stop an enemy that is trying to run away.

Early game you should stick to farming and harrasing your oponent.

Dont use Hail of Arrows to farm too much especially before you hit lvl 6 or you will run out of mana to quick.

This is some of my past match history as Varus