Hi and welcome, this is a simple Ashe build which i use and would recommend to new players or experienced players.

Exhaust is a major spell in both early game and late game as it can be used to slow enemies for you and your teammate to grab that first blood but also to slow the one more enemy champ to grab that late game ace to push and end the game.

Ignite can be used at the same time as exhaust so then they are slowed and damage whilst you can deal allot of burst damage with the build.

For your rune i have given you the choice but if your not sure i would just take either Critical Chance, flat damage or Armour penetration, a mix of 2 out of the three should be effective.

Pros- you can easily Spam your W to do allot of burst damage whilst slowing them with your passive q so i would recommend playing on the bottom lane with another champion that could do damage or tank to take some of the damage of you.

Cons- you can deal some damage in early game but not as much as in the late game so try to stick with someone who will easily back up kills for the first blood and early game feeds.
You are also quite squishy until you grab the Frozen mallet so you might want to grab that earlier instead of, for example, the phantom dancer. You could also try playing with a tank to curve some damage away from you

Doran's blade- this is for early game damage and is the best in my opinion starting item for ashe.

Boots of swiftness- your going to carry the kills so you need to move around allot quicker than both your enemies and allies.

Infinity edge- this is a must buy as you need the extra damage and this supports the crit chance and damage from your Phantom dancer to deal allot of damage based on basics.

Phantom Dancer- This is also a must buy as you need the attack speed to get the last hits on both Champs and minions and the crit chance is supported by your Infinity edge and the extra movement speed is needed to chase.

Frozen Mallet- this gives you your basis of survive-ability as it gives you much needed health and Damage. The passive on this item helps with chases as it slows and matches well with your q.

Last Whisper- this item gives a boost of damage and also Armour pen to pick of the more armored champs in team fights and lane fights

An item that i have been testing is Tiamat, this is good as it gives more damage than doran's blade and also has attributes such as Mana and Health regen