i'll explain in very simple words.

forget dorans dagger its useless. get boots and 3x potions for early game. you will be focused a lot.
try to get 1 phantom before anything else. other than the boots
then aim for infinite edge, but get B.F first so it'll be cheaper
get black cleaver for some hardcore penetration. it bumps armor pent. atk spd and dmg
go for twin dancers then bloodthirster for self heals
i perfer flash than teleport because it helps you tower dive and get our of sticky situations. and flash is a no brainer. i dont need to explain.

early you will be focused because ashe is just squishy early game, have potions. i perfer atk speed before atk dmg because you have frost shot which is very good for kiting, slowing, and just picking out single champs.
i play Lol at 10-15 fps and that is just too difficult to do skill shots. so i sometimes go for ludicity instead of berserkers. dancer/edge combo is killer, it rapes mid game and then add black cleaver to just put pressure.
twin dancers are essential and you really just need one bloodthirster. hopefully the game doesnt end before you get all your equipment.

ashe is a ranged ad archer that has a mana bar. i know it sucks but you have to deal with it. I suggest to not use volley that often either to slow multiple champs or get last hit. dont waste it on minions unless its late game and on tall grass, your mana will drain. i max frost shot because you do almost everything, you slow and your team do easy pickings. you want others to be fed because ashe can handle herself unlike the others. her ult freezes, frost shot kiting, volley is very annoying. and that hawkshot is just too good. i can find ppl hiding in the tall grass without going over there.

when using ashe be patient, dont rush or you'll die in a sec. dont ult immediatly unless your chasing as a group, just toggle frost shot and ghost to them. i love tower diving, if a champ is on low hp, wait for your minions and flash to them or ghost and do a couple of last hits and dip. ghost is sooo good early and mid game. late game is just shows whos stronger