Ashe as a support isn't played that often, which is strange as she is described as: secondary support on her character description. The main support attributes to Ashe include: her passive for early high damage pokes, her Q for slowing enemies enough for your ADC to secure kills, her W also for early high damage and the added slow effect, her E for extra vision when you think you lane could be ganked, and her Ultimate for when you want to engage the opponent with high damage and the awesomeness that is the stun >:{D

Early game, it's a great idea to save your passive, partly because as support you shouldn't be hitting minions anyway, and also because you want to save those high damage critical hits for hitting enemy ADC's (or humorously squishy supports). The Mastery's and Runes I have set up in this build as sure to make those early game passive pokes very damaging, and they will also make you laugh uncontrollably as your lane is won with a few pokes X{D

Mid game, you should be looking towards hitting enemies as much as possible, either safely with your Volley or up close and personal with your passive pokes and Frost shot, keeping your enemies slowed enough for your ADC to stack high amounts of kills >:{D

Late game, as well as throughout the game, you warding will help win team fights: make sure you at least ward dragon and baron so that you know when lanes will be ganked and when those epic monsters will be contested! Also, every now and again when you haven't seen an enemy for a while, just randomly shoot your hawkshot through the jungle, it could supply your team with an additional kill or save the lives of your closest team-mates if the enemy is preparing an ambush :{o

An additional note: Your enchanted crystal arrow is an awesome engage tool, you can start off team-fights with your ultimate and the stun effect could help your team come out on top by a large margin :{D

As you are a support, farming shouldn't be on your mind, but farming should be relatively easy if your ADC is out of lane and you have some spare mana: just let off a few volleys (no-one will notice o.O) X{D