Here’s one quick look on a Ashe guide by TSM Chaox!
 
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Frost Shot |  |
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Volley | |
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Hawkshot | |
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Enchanted Crystal Arrow | |
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if you have sustain (soraka, sona, alistar)
if you lack sustain (janna, blitz, nunu)
Doran’s is sometimes acceptable even if you don’t have sustain on your support, since it increases your lv1 crit damage significantly and you can gain an early advantage and can deal with harass with merely the extra 3% life steal.
[Early game goals]
optional: 
You don’t want to make Bloodthirster on Ashe unless it’s one of your last items. The vamp scepter is incase you need that extra sustain in lane, or vs a poke team for dragon fights.
[Mid game goals]
+ 
or 
Infinity first is standard, after that there a interesting level of optimization.
first against full squishies.
if 3 or more enemies have over 100 armor
+ if you started on PD, and then enemies bought armor.
[End game goals]
Optimal End-Game AD, perfect balance of offense and defense.
For a full review please check on their website! The website : http://www.solomid.net/guides.php?g=17118
