Focus will allow you to land a guaranteed critical strike on your first shot of the game. Choose whether to use on a champion instead of on a minion. This shot in conjunction with Volley can provide substantial burst damage and give you the edge in a level one engagement.
Volley has a fairly large cone and decent damage early/mid game. Use this to your advantage by positioning yourself to last hit minions and harass the enemy champions with it. Avoid spamming it early game as you most likely end up pushing the minions to the enemy tower.
Volley diminishes quickly in the late game; however, it still provides a great deal of utility. Volley can slow a great majority of the enemy team, can still be used between autoattacks, hit enemy chasing/retreating in bushes, and more importantly, Volley can pop Banshee's Veils.
Keep in mind that champions with dash abilities can counter this tactic.
If you are having mana problems then alternating Frost Shot so it only activates every 2nd attack might help conserve mana while constantly applying the slow.
Use Hawkshot to check the nearby jungle for enemies that may be attempting to gank you. It is also useful to check if the enemy is fighting the Dragon or Baron Nashor from a distance.
If your team is engaging either of those monsters, Hawkshot will give you advance notice of enemy approach, but also inform them of your general location.
You can use Enchanted Crystal Arrow to help your allies from another lane. If your allies have the advantage, shoot it further up their enemies' lane, and if not, aim further down your allies' lane. This can give your allies the opportunity to strike a killing blow or make a getaway. However keep in mind that there is a low chance you'll hit them and you lose a lot of lane control if your opponent knows it's on cooldown.
Enchanted Crystal Arrow is one of the best initiators in the game, able to stun an enemy (preferably someone squishy) from a distance.
Enchanted Crystal Arrow is also a great skill for ganking. A well aimed arrow can stun the target long enough for you or your jungler to apply their CC as well. Furthermore, Ashe's passive usually guarantees a critical hit if she has been traveling between lanes.
Enchanted Crystal Arrow is also a great skill when your opponents are losing the match and are running/escaping. Using it at the right moment can slow the whole team down, grabbing yourself an ace.
When shooting Enchanted Crystal Arrow towards another lane ping the area it will hit. This will alert your teammates that you have shot your ultimate.
Don't be afraid to use Enchanted Crystal Arrow to escape, however be aware that the duration of the stun is based upon how far the arrow has traveled before impact.
Try to fire Enchanted Crystal Arrow in the same direction enemies are moving, so it is more likely to land a hit. It has a surprisingly large hitbox.
Ashe is one of the weakest 1v1 characters in the game when she decides to stand and fight. Assuming your opponent is as farmed as you are, Ashe is outdamaged by nearly every other ranged AD character, quickly assassinated by nukers/bruisers if caught out of position, and heavily CC'd by tanks that she takes a long time to kill.
Her strength heavily relies on her ability to kite enemies and punish enemies out of position in team fights with her slow.
Building Ashe as support is not ineffective as she does have a very low damage output. Building auras and cooldown reduction is an extremely effective way to play her. With her perma-slow, cone slow, vision, AMAZING stun, and requirement to be in the back during a team fight, she can do just fine supporting her team.
Statikk Shiv synergizes extremely well with Ashe because of Focus : As it can critically strike, staying out of combat long enough will transform the next auto-attack into an hybrid physical/magical burst.
Ashe mainly deals damage by using auto-attacks, so buying Thornmail can help counter or even kill if she has low health.
Although Ashe is a great harasser during the laning phase, her low health is a great disadvantage. Putting pressure on her can keep her zoned.
Being tied for the lowest movement speed for champions in the game leaves Ashe vulnerable to skillshots.
Ashe has little to no defensive capabilities. Use this to your advantage. However, she can slow you constantly as long as she has mana, so wait before she is low before you go in to kill.
Gap-closers can quickly take advantage of this, since her slows cannot counter them.
Watch for when Ashe uses her Hawkshot. This tells what part of the map her team has no vision of.
At the same time, beware for the inverse. You might be tricked into thinking an area is unwarded because she just used her Hawkshot, while it was just used to lure you there after the effects wore off.