Hello! What a wonderful day! Lets get started. this is my very first build, leave any suggestions BELOW! Thank you.
Also, please read the guide very carefully. It is a guide about Attack speed and armor penetration.
I hope you enjoy, please notify me at any modifications i should make.

First off, Ashe is slow as hell, get boots of speed and 3 health potions. makes you stay in lane longer. Get a Doran's blade, sell it afterwards if needed. The infinity edge is a great damage output, get that! Afterwards, you want to be faster, get boots of swiftness.
Phantom dancer for more damage and attack speed. last whisper for armor pen. Black cleaver or bloodthirster are very good, too. Get all of that, and don't forget to buy hp pots and wards if nessecary.
NOT UPDATED AS OF NOW

Not much to say here, max volley as soon as possible, and frost shot. Whenever you can, max the enchanted crystal arrow. Lastly is the unimportant Hawk shot, skill it before frost shot if you're very bad at last hitting minions, and every penny counts. Skill wisely. Everything is optional, so you can skill frost shot after Hawkshot, but Volley should be maxed first. Keep that in mind!

Ashe without volley is a plate without food on it It is NOT important though for last hitting minions,so don't waste it, your mana will drain VERY quickly.

Flash for escaping, and Clarity for the case that you still have full hp in a battle, but no more mana to fire your ultimate to finish your enemy off, use clarity. Alternative: Take ghost or exhaust instead of clarity for an even quicker way of getting out of situations if your flash is not ready.

!Ashes Masteries should be 21/9/0. First off, if using exhaust, skill cripple, otherwise skill archmages savy. Alacrity for atk speed,Sunder is needed for Armor pen., and skill something you need for Brute force, max that. Max Lethality and Havoc. For Defense, use Hardiness on max,resistance, and strenght of spirit. Masteries make a great portion of the gameplay and early advantages

Attack speed runes are for faster downing of enemies and the Armor penetration is defently needed, get that. It is very important to take speed, but if you want, you can take critical chance runes.
Runes. ONLY buy tier 3 runes, so when you're lvl 20. if you are under lvl 20, dont even bother...
UNUPDATED

Usually you are alone on mid. but when you are at top with someone (or bottom) and they are a tank, stand behind them and attack from behind them. if they get attacked, you wont. If you are 2 ranged people on either side, try to alternate your skills or attacks, confusing the enemy. If you want to jungle because there are no lane minions, make sure to have a friend with you or you could die very easy. By a gank.

PROS: This is a good (in my opinion) harass build. It allows you to attack quickly and strong, making opponents fall back.Your damage will slowly build up. You need that armor penetration to make the damage more effective, which makes team fights as simple as waiting and standing.
CONS: Ashe is always very squishy. Make sure you don't turret dive, dive into team fights or anything else lethal. Without armor penetration, this is partly bad for you as you don't deal as much damage, if the enemy team deals too much damage get some defense!

It is not very easy to last hit, but here is a quick guide JUST for Ashe. with your level 1 character, alone in mid (usually) you deal only about 60~61 damage. let your minions weaken the enemy minions, and you finish them off with a last hit. if there is a group of weakened minions, use volley to instantly kill all of them and get all of the gold. The annoying thing is auto attack. Try to keep moving to avoid hitting the minions.