This won't be a very in depth guide, as it is my first guide, but I think that the above build is the best for Ashe.

For runes, I choose Greater Mark of Desperation for the nice armor pen, Greater Seal of Regeneration to give Ashe a little more sustain, Greater Glyph of Replenishment to help her spam her Volley, and Greater Quintessence of Desolation to give her some more armor pen.

I did 21-9-0 for masteries in order to give Ashe some nice boosts to her attack, but she also gets her squishiness reduced some with this.

I always start Doran's Blade with Ashe to give her a little more oomph. From there, I get Berserker's Greaves, that way she can move and attack more quickly. Then, I get Vampiric Scepter, so she can get some more sustain and to start building Wriggle's Lantern. Next, I get Madred's Razors, and then I finish off Wriggle's Lantern, which is perfect for her because it gives her lifesteal for sustain, defense to survive fights, and AD to help her killing power. Next, I get Zeal for the boost in crit, movement, and attack speed, after which I get Phantom Dancer, to further that boost. Next I get Infinity Edge, that way she can get some more AD and it also enhances her passive. Then I get Frozen Mallet, to help out her Q and W, finally finishing it off with Bloodthirster, to give her lifesteal and AD a nice boost. At the end of the game, you may want to swap out your Berserker's Greaves for another Phantom Dancer, although you will rarely make it that far.

Her passive is Focus, which slowly increases your crit chance when not in battle. You first want to get a point in Volley, since that is your main harassing attack. Then you get a point in Frost Shot to enhance your Volley, and to use on its own. Then you go back to Volley, and then take a point in Hawkshot. From there, get Volley to level 4, taking Enchanted Crystal Arrow at 6, and then get Frost Shot to 3, because at 1 it doesn't do too much. Once Frost Shot is at 3, finish up Volley then take another point in Enchanted Crystal Arrow. Finally, max out Hawkshot, taking Enchanted Crystal Arrow at 16.

I use Ghost because Flash got nerfed, it provides a good means of escape or chasing. I use Ignite to finish off those pesky champs that hide behind their turret.