First champion that I've played and is still a big time favorite of mine. I hope you enjoy my first go at sharing a build with all of you who play with me upon the Fields of Justice.

Although I've set mine with Armor Penetration Quints if you feel that other runes would be appropriate feel free to deviate.

Ghost and Clarity are the 2 spells I feel do the job when playing Ashe.
Exhaust is redundant if you get your Frost Shots going.
Ignite does so little compaired to the havoc you can reap when your opponent is slowed.
Heal may be a good replacement if you play more passively then this build requires. But with the lifesteal benefits I doubt it'll be useful if you play her well.

This Ashe is MADE for mid but can do well anywhere. Your first goal is surviving. Ashe is not tough, nor is she a nuke. The boots you get first will help you dodge enemy abilities and position yourself for your "Volleys". Always try to get 5 of your 7 arrows to hit. If you're aiming to hit your opponent go for 3/7.
Harass when able but try to avoid minion damage. Don't be afraid to waste mana. Clarity is there for that. Remember, minions are friends. Kill your opponents' and drive them back. Do not try to go for the kill til after you have your ultimate. By then you should have decent lifesteal and damage.
Once you have the sttack speed, critical, and movement speed bonuses from the zeals start chasing. Frost Shot will stop enemies from ever getting away even when they have flash or a skill that lets them do so. If needed use Ghost.
By the time you have either 2 Phantom Dancers or 1 and Infinity Edge you should be able to 1v1 any opponent in good conditions (e.i. no minions, ganks, or turrets). Remember to keep your Bloodtthirster stacked and if you feel confident let loose your Enchaned Arrow to help other lanes. Practice reading enemy movements will help you gain assists even from across the map.

Basically you start out passive. Never actively engaging your opponent, always trying to nick them a bit with your volley. However that doesn't mean that you should chicken out if Ez decides to flash into you and your minions. Always look for a cheap shot in, stack the damage over time, never get greedy.
You're Ashe, the Frost Archer. Being hasty never gets you your kill. You move around dodging skills and aiming to slowly cut down on your opponent by wittling away at their health.
By the time you get your ultimate why chase? One good shot and chasing is all you'll have to do to kill.
Towards the end you'll be quick enough to chase anything that moves and punishing enough to kill quickly.