Depending on preference & whom is supporting you, you can take heal or ignite.

Runes are fairly standard, Armour Pen a pretty much must, Armour as they will undoubtedly have Armour Pen, Magic Resist (Simply because if the Jungler isn't AP their mid is!) and finally Attack Damage.

I start with boots, because ashe isn't the most mobile of all the AD carries out there and its not hard for an opponent adc or support to keep up otherwise.

Damage comes next, dorans blade is a good item, as its both damage and health as well as a little of health regen while attacking (every little helps). More damage comes in the form of the vamperic scepter as well as much needed lifesteal.

Bezerker Greaves I tend to go for next, as it gives both attack speed which were working on now as well as additional movement. This should keep you farming and possibly killing until you can get the much needed damage of the holy BF Sword. Now were talking!!

From here you can change things as required but the build is like this for one reason. statikk shiv gives similar attack speed and crit chance as phantom dancer (slihtly less) but gives a bit better movement speed, as well as enabling you as a adc to do magic damage! of which can also crit! also allows you to farm easier.

Infinity edge is pretty much ashes must have item above all else, attack damage... crit damage and crit chance! The next 3 things I work towards are in parts just so you get a bit of everything, particularly the health!

Bloodthirster, much needed damage & lifesteal, ruunans hurricane, attack speed as well as free extra damage to surrounding targets, and finally warmongs, for as much health as you can get in one item.