This is how you own with Ashe. I maintain over 65% wins with Ashe and have played with her over 100 games. I can't guarantee this is the best build ever, but it serves me very well. Your Priorities are Crit Damage/Normal Damage, Using that first 100% crit shot, Using your volley properly, Crit%/Attack Speed.
Ghost: This is really important for Ashe, as she is a slow character. This helps with tower diving (yes you can dive with Ashe if you know you can finish off the opponent quick) as well as helping with escape and team fights. I have seen many people use flash instead, and this works too however, it doesn't have as much use in team fights. Ashe needs to stay out of the middle of team fights and Ghost allows her to hit and run to avoid becoming the other team's main target.
Heal: I know many of you are probably screaming NOOB right now, but I can't tell you how many people I goad into tower diving on me only to see me heal and ult them at the tower. Heal is a really good spell for DPS chars as they should never be aiming to get high max HP, thus the Heal will always return a decent percentage of their health.
New Addition: Flash: I have recently been going back and forth between heal and flash. Heal is great for luring and I often trap players with it, however Flash is really good if you are feeling extra aggressive. I have started getting more and more aggressive with Ashe (not sure if this is a good thing), but definately experiment to figure out what you like better.
Rune Build: You can experiment with a lot of these, but for Ashe, she is a Crit fanatic and I really like boosting that crit damage. Other DPS rangers like Teemo or Tristana can go for Attack speed or pure damage, but Ashe should really be built around her Crits. Do not go crit damage for all three sets. The Marks give a large percentage of that crit damage, so the other two sets should be built around other things. I like dodge and cooldown reduction, but try out others if you think you can do better.
Passive: Crit % increase while not attacking. First of all, this is awesome. Do not forget about it. Right off the bat when you go to solo middle (because that's what you SHOULD be doing), do not waste this shot on a critter. Hold off hitting the critters and go aggressive with this first crit at your opponent that should hit for about 120ish if you built her the way I said. This paired with a volley at the same time should drop them to half health right off the bat. This is Ashe's money shot so don't waste it trying to get 24 gold. After you drop them to half health, believe me when I say it's going to be easy to keep them off the creeps. They will know you mean business and do not intend to let them solo well.
Volley: This is not PRIMARILY a farming tool. Far too often, I see Ashes against me wasting their volley on the creeps while I hold mine against them like a gun to their head causing them to back up. It should be a constant threat for them. Walk around the creeps a bit and make sure you hit them with this. Once you get your first level of frost shot, this will add frost to every arrow in the volley, so you can hit them with the volley, walk up, hit them once or twice, back off a bit and see how they react. You will notice they start tower hugging quite a bit. Continue to pepper them whenever they leave their tower range, you own the lane and make them respect you.
Frost Shot: Slows, use your q only when someone is going to run or you have lots of mana that you don't mind wasting. It is more important that you hit your volley as it does both damage and the frost.
Plentiful Bounty: Pretty much useless. It helps for extra gold in late game to really pile on your items, but in general, bleh.
Enchanted Crystal Arrow: Awesome. Nuff Said. Make sure you lead people. And if you have been playing the volley properly, you should be able to finish off a kill at level 6 almost immediately. I would say about 70% of my games I get a kill as soon as I hit level 6. This also does a bit of aoe damage, but try not to fire it into a crowd. I know it's tempting, but it's more useful if you can pick someone off who comes a bit too far from their teammates. It's also a really useful counter to many Heroes like Yi, Nunu, Fiddle, etc. Use it as a tool in the team fights, not as damage.
Don't go life steal first. I see a lot of Ashe builds saying to do this. This doesn't make any sense when you consider the fact that she owns lanes by that first crit and the volley. Her attack speed is low early game as well as her normal damage, thus you wont be stealing much life. You should be last hitting creeps, not continuously hitting them. You will be allowing the enemy to lane with you, which is stupid. You need to be able to use that volley often and still save up mana for your ult at level 6. So that means mana regen!
Philosopher stone/Meki are useful early due to the mana regen and the added gold is nice (I prefer it to the challice due to the gold and health regen that keep you in lanes longer and get you the better items quicker). (Grab two health pots with the meki right off the bat to keep you rocking your mid solo lane). Remember the meki will help you with being able to constantly use your volley, which is key to getting the upper hand with Ashe early.
Berserkers Greeves: I rarely go with any other boots for her. However, there have been a few games where I noticed I was playing a really strong caster team and I'd opt for mercury treads. (If you get mercury, it means getting zeal next for the attack speed).
Infinity Edge: Crit % and Crit damage as well as awesome normal damage added. This will get your crits hitting for 500 in the mid game which very few chars will be able to handle.
Blood Thirster: I've been experimenting with getting the sceptor before infinity edge lately just for the added lifesteal through mid game and it seems to be a good idea, but do not finish the BT before the IE. Get the IE first due to the crit % and crit damage. BT is a great next item for building up damage.
Black Cleaver: If you are playing a heavily armored team, I will sometimes choose the Last Whisper instead, but this item adds a **** load of damage and helps the team more (as it reduces the armor for everyone).
Zeal/Phantom Dancer: If you want to get Zeal before the Blood Thirster, that makes sense, but do not finish off a Phantom Dancer mid game. This item is super expensive and should only be added after you have built up your damage. The dodge percentage and added attack speed will only add to your domination (but alone without damage to start with, it is hardly useful).
Finally you want to replace that philosophers stone. If you have all of your items, you don't need the gold production. I like to make some decisions at this point. If the team is getting caster-effed, I'd go with Banshee's Veil, but if you are okay without that, grab another Blood thirster. You will be critting for 1100 damage if you do this, which is rediculous especially given your first hit will be 100% crit. GG
If you are REALLY raping early game, The sword of the occult is a cheap purchase you can grab right before the infinity edge, which will increase your crit damage by a lot and thus increase your advantage.
If you have any suggestions, feel free to comment, but I think I have got Ashe down to a science at this point. I'd make a teemo build, but they're all the same, so I may move on to Pantheon as soon as I can get him up to a 60% win percentage.
Note: I am aware that the build is out of date now to some extent, I have just started playing LoL again, so I will fix it when I get good again. (been playing lots of SC2 lately)