Ashe is a high damage ADC whom is my favorite ADC to play. Keep in mind that Ashe has no escapes... So positioning is super essential in teamfights. Keep your distance and use you range to you advantage. Farm as normal, and use your passive to harass enemies with a high damage crit shot, and if early game level one encounters occur. This will definitely tip the scales in your favor.

1:W
2:Q
3:E
4:w
5:w
6:w
7:q
And so on, Max W first, then Q, then E, and upgrade R when possible.

Your R/THe mighty Ashe Arrow:D is what makes you a very viable ADC. Using your ult to start a teamfight or to chase enimies as they flee in terror is a great way to win that fight. The AOE stun and decent damage is just overall a game changer in fights.

Runes, just your standard ADC ones,and masteries etc.
ALthough I would advise to get like 5% crit from runes just for that early game :P
And masteries, Majoring in Offensive, all the AD and Havoc, And spend left over points in defense for block(reduces enemy auto attacks).