This is a build for Ashe, but the item build is standard, and can be used for many/most ad carries.

AD marks for easier last hitting earlygame, and easier poke easygame. Make sure to get Last Whisper if you run AD marks though.

Armor seals for sustain and to resist poke/fights from the enemy ad carry.

Magic resist (/Magic resist/lv) glyphs for lategame/for the poke from their support in lane.

Movement speed quints for being able to get boots later on without loosing out of the movement speed. AD quints give you ~5 ad, boots give you +25 ms, while the runes give you +3.5% ms (=~11.4 ms for Ashe). However you get +10 ad for the long sword, which is 5 ad more than what you would have gotte from the ad quints.

21/9/0 because:
- Basic 21 offense.
- Some free armor + hp

This is what I call a standard ad carry build. This build works for most ad carries.

I max w for early dmg and poke, max q second for kiting and e last. Make sure to save your arrow for initiation late game. Remember: The longer the range the arrow is shot from, the longer the stun.

You can also go flash + (exhaust, heal, ghost). Let the support take exhaust/flash.