CORE BUILD

The usual start is either Boots and 3 Health pots or Doran's Blade. Most of the time you will be getting at least 1 Doran's during the game. This is for the HP/DMG/LifeSteal. If you are finding that the enemy RangeAD is ahead of you in farm/kills/owning you, grab more Doran's. I usually get 3 at most if I'm behind and need to catch up.

A normal build progression would be:
Boots + 3 Pots
Doran's
Dagger (20% AS)
Berserkers Greaves
BF Sword
Pickaxe
Cloak of Agility
Dagger
Brawler's Gloves
Zeal
Phantom Dancer

The order is not exact, can be fudged around depending on how much gold you have. Priority in building Infinity Edge is BF Sword, Pickaxe, then Cloak. Dagger over Brawler's Gloves in building Zeal.

GAME DEPENDENT OFFENSIVE ITEMS

Last Whisper if enemy team is building armor.
Bloodthirster if you are getting in a lot of light skirmishes/trading and or have the cash.
Zeal into 2nd Phantom Dancer if you play like me and like to play defensively and kite a lot.
Black Cleaver if you are feeling overconfident.

GAME DEPENDENT DEFENSIVE ITEMS

Banshee's Veil if heavy caster/lots of spells, Guardian Angel if you are targeted a lot/your team can't stop them/its super late game

RUNES

Attack Damage Reds
Armor Yellows (I like to add in some HP/lvl)
MR per Level Blues
Attack Damage Quints

MASTERIES

-- 21/9/0 --- The only way to go.

SUMMONER SPELLS

AND

OR

Flash is the most important for obvious reasons. Heal or Exhaust depending on your lane opposition. If you want to be aggressive, or stop them from being aggressive, grab exhaust. If you know you can kind of hang back and farm, heal.

PROTIPS

1. Wards are your best friend. 75 gold for maphack. Highest return of any item.
2. Don't overextend unless you can locate the other members of their team that are not near you. Warding helps in overextending.
3. Stay behind your team. You are Ashe, you shoot things, you don't let things shoot you.
4. Don't jump the gun on your ult. First run back a few steps, this puts you offscreen of some people and makes the arrow take longer to get there, making the stun longer. Move to the left and right to get a better angle on the squishies.
5. Use volley sparingly early on. With this build you should barely ever run out of mana; if you are finding that you are running out constantly, you are volleying too much or leaving q on.