The 2 spells I bring with Ashe are Cleanse and Flash. Cleanse lets me get away when I have been slowed or stunned because it removes any disables (excluding Supression) and summoner debuffs affecting your champion. It also makes grants you 65% CC reduction for 3 seconds. Since Ashe is SUPER squishy all game, I bring it with me and it saves me at least 2-3 deaths a game.

Flash is almost a no-brainer to bring for anyone. It can help you escape by poofing through walls and jukeing out an opponent. A combo with these 2 can change a game and keep you from dying.

The Runes you want to grab are 3 Greater Attack Damage Quintessences, 9 Greater Marks of Armor Penetration, 9 Greater Seals of Armor, and 9 Glyphs of Magic Resistance.

The 3 Greater Quintessences of Attack Damage are pretty obvious for a ADC. What are they? Attack Damage Carries. What do they build? Attack Damage. Each Quintessence is +2.25 Attack Damage. 2.25 * 3 is 6.75 EXTRA Attack Damage at Level 1. I think that is pretty nifty huh?
The 9 Greater Marks of Armor Penetration are also kind of a no-brainer. As a ADC you want to maximize your possible damage output. The Greater Marks of Armor Penetration make that possible by being able to penetrate your opponents armor. Each Greater Mark of Armor Penetration is +1.28 Armor Penetration. 1.28 * 9 is 11.52. Good chance that is probably 11.52 more Armor Penetration early game then your opponent in a Non-Ranked game.
The 9 Greater Seals of Armor let you sustain in lane better. You will be taking less Physical Damage because you have more Armor early in the game. If your able to sustain a lane, which means to be in longer before your opponent before you have to recall, you get a HUGE advantage. You will probably be 1-3 levels higher then the enemy because you were in lane farming for a longer time. Each Greater Seal gives you +1.41 Armor. 1.41 * 9 is 12.69. As I said earlier, good chance you get 12.69 more Armor then your opponent early game.
The 9 Greater Seals of Magic Resistance let you also sustain a lane longer. If the Support is doing the poking instead of the ADC, you don't have to worry. Each Greater Glyph of Magic Resist gives +1.34 Magic Resist. 1.34 * 9 is 10.34. That is 10.34 EXTRA MAGIC RESIST! As stated before, the more sustain you have, the bigger advantage you have.

The Masteries you want are 21-0-9. This means 21 in the Offense Tree, 0 in the Defense Tree, and 9 in the Utility Tree. Below are the Masteries you want.

Attack Tree

Fury increases your Attack Speed. With 4 points it increases your Attack Speed by 4% This allows more Damage Per Second.
Deadliness increases your Attack Damage per level. At level 18, with 4 points in it, you gain +12 Attack Damage at level 18.
Weapon Expertise gives you +8% Armor Penatraton.
Havoc increases damage dealt by ~0.67% per point. With 3 points it grants you 2% more damage.
Brute Force grants more Attack Damage. Each point gives you +1.5 Damage. With 2 points it gives you +3 Attack Damage.
leathality increases your Critical Strike Damage. Not Chance. Each point gives you +2.5%. With 2 points you gain +5% Critical Strike Damage. This bonus is doubled with Melee Champions.
Frenzy grants you 10% attack speed for 2 seconds after landing a Critical Hit. This is extremely helpful for Ashe to maximize DPS because she will be landing a lot of Critical Strikes.
Sunder grants +2 Armor Penetration for each point. With 3 points it grants +6 Armor Penetration.
Executioner increases damage by 5% to targets below 50% Health. This is incredibly helpful for AD Carries because their damage is already high and this maximizes their full potential when this is selected.

Utility Tree

Improved Recall allows you to teleport to base a second faster.
Wanderer grants +2.00 increased Movement Speed when out of combat with all 3 points. +0.66% per point.
Summoner's Insight improves several Summonder Spells, but we're looking at Flash. This mastery reduces the cooldown of Flash by 15 seconds.
Mastermind reduces the cooldown of Summoner Spells by 4/7/10% depending how many points are in it.
Runic Affinity increases the duration of shrine, relic, quest, and neutral monster buffs by 20%.

Passive - Focus

Focus lets Ashe's Critical Strike Chance increase by 3/6/9/12/15/18% every 3 seconds when not attacking. Focus' bonus is used with her next basic attack.

Q - Frost Shot

Frost Shot TOGGLE: Ashe's basic attacks slow her target for 2 seconds. You have to turn this on. When active, it drains 8 mana per attack. This ability has no cooldown.

W - Volley

Volley When used, Ashe fires 7 arrows in a cone, each arrow dealing 40/50/60/70/80(+100% AD) to each target hit. Each arrow will only hit one enemy, and each enemy will only be hit by one arrow. Volley also applies the current rank of Frost Shot, regardless of it is toggled on or not. The arrows fly at a speed of 2000 and the cone is 57.5º. This ability has a cooldown of 16/13/10/7/4 seconds and costs 60 mana.

E - Hawkshot

Hawkshot Passive: Ashe gains 1/2/3/4/5 bonus gold whenever she kills a unit or destroys a structure. (A structure is a Heimerdinger turret, etc.) This is useful for farming.
Active: Ashe animates a hawk to scout for her, revealing terrain for 2 seconds as it flies toward a target location. Hawkshot reveals a wide area for 5 seconds when it reaches its destination. The Hawk will reveal units in the brushes, but will not reveal stealthed units or objects. The range of Hawkshot is 2500/3250/4000/4750/5500 units and has a 60 second cooldown. It costs no mana.

R - Enchanted Crystal Arrow

Enchanted Crystal ArrowWhen used, Ashe fires a 1600-speed large arrow in a straight line. If it hits an enemy champion, it will deal magic damage and stun that champion for 1 to 3.5 seconds based on the distance of the arrow traveled, reaching max stun duration at 2800 units traveled. Additionally, enemies within 125 range of the impact take half the damage and are slowed by 50% for 3 seconds. The arrow deals 250/425/600(+100% AP). The range of this ability is global, meaning it has to max range. The cooldown period is 100/90/80 seconds and costs 150 mana.

Spawn

Right when you spawn, grab Boots and 2 Health Potion. If you have a Healing Support like , , or , grab Doran's Blade

Early Game

Life Steal is essential at this point. The enemies will be exchanging blows because they probably have more items. So I would by a Vampiric Scepter, upgrade my Boots to Berserker's Greaves, and purchase a Doran's Blade if you haven't already.

Mid Game

At this point, you and the enemy are both getting the builds about half way complete. So damage will leave a mark. At this point, having more items that provide good bonuses is key. These next couple items, if you can get them all, will help you immensly. I would build to a Infinity Edge. This provides you with a hefty +70 AD, 25% increased Critical Strike Chance, and Critical Strikes do 250% damage. This is needed for almost EVERY ADC Champion. Plus with Ashe's passive "Focus" you will be landing Critical Hits like crazy. The second item I would build toward is a Phantom Dancer. This increases your Attack Speed by 50%, gives you a 30% Critical Strike Chance, and a 5% Movement Speed increase. (Psst. Ashe is slow AF!). At this point you are at a 55% Critical Strike Chance. That's roughly 1 in 2 attack lands a Critical Strike! My next item would be a Last Whisper. This gives a decent +40 AD but a whopping +35% Armor Penetration! That is about 35% MORE DAMAGE! But I'm not done yet. The last essential item would be the Black Cleaver. This gives a massive +55 AD with a OK 10% Cooldown Reduction. It also includes a free +200 Health and a Unique Passive. Its Unique Passive gives a +10 Armor Penetration (Pretty Nice) and dealing physical damage to an enemy champion reduces their armor by 5% for 4 seconds. This effect stacks up to 5 times. When all 5 stacks on on, it reduces their armor by 25%! MORE DAMAGE!

Farming with Ashe is extremely easy. Make sure to use Volley to clear a minion wave and get gold to come in. Ashe's Hawkshot is similar to Twisted Fate's passive. His passive lets all allied champions gain an additional 2 gold per kill. Ashe's E is 2.5x better then his passive when the E is maxed out. Be sure to abuse this ability in Laning Phase.

Ashe isn't very strong in the Laning Phase. When she gets her CS up and/or is fed, she will dominate everyone. She will easily get kills because of her slow with Frost Shot. The tip is to get them running. When they start to run away, get at a comfortable distance and continue to hit and slow till you kill them.

In team fights, you do not want to be the first one in. That is the tank's job. Naturally every one will want to focus you because you are the AD Carry. To counter this, use a Volley to slow them and find a comfortable distance to engage. Another method is coming in late when the fight had already started and using your Enchanted Crystal Arrow to stun and get some good damage off. When you get your full build, you will be dealing 400-500ish damage consistantly at a fast rate. If you die because everyone piles you, it's most of the time not your fault. It is your teams job to keep you alive. If you die, 70% chance your team loses the fight. YOU are the main source of damage. You are called a "Carry' aren't you? You carry the team to victory.

Ashe can be a vary fun champion to play and troll with. The main troll is her Q and W. But as with all the other champions she has her strengths and weaknesses.

PROS

-Amazing Slow With Her Frost Shot and Volley
-Great Ult to Snipe Champs Across the Map
-Great Farmer
-Unstoppable If Fed Early

Cons

-VERY Squishy Early Game. Not as Squishy Later
-Few/None Escape Routes If Ganked Perfectly
-Needs a Healing Support like or to sustain in Laning Phase