Read Before Playing. The above Skill sequence reflects ashe middle, not lane

Pros
--Great Ult
--Perma Slow
--Good Late game
--Scouting
--Carry

Cons
--Squishy
--Relies heavily on a well placed ult
--No reliable escape mechanism
--Most builds rely on crit dmg and crist % and her passive
--Fairly item dependent.

Ashe is a great champ, after playing literally 100s of games with her, I finally think I have mastered her, and will share what I know as best I can with you. I initially started playing her witch still very popular "true ranked carry." This take on Ashe emphasizes move speed and high damage with a high percent crit chance.

It is important to use primary runes when playing any champ. Look for a guide on runes if your confused on the meaning. Primary runes mean you get a large boost than secondary. I have chosen all primary to max the boost. All the runes I have listed here are very useful and are good on many other champs. I.E. CD runes I use them on my caster guys and another example Dodge goes really well on a tank if you do get hp or armor.
This is by no means the only way to play Ashe, but it is a good starting point. Armor pens to help your auto attack, these also help ur crits. Armor pen are generally considered better than crit dmg because mathematically armor pen runes produce higher dmg than crit dmg even while on crits, I'm not making this up, any good guide on runes say so.

Dodge Seals, a nice unique runes could save your life. There are many other good choices for seals. Mana regen seals is a useful alternative if you consistently drain your mana pool.

Glyphs CD runes. Helps with your volley and ult. A good second choice is Attack speed, although AS glyphs are secondary.

Quints More armor pen. Additional armor pen is nice. Flat health quints is also a good boost to early game.

Read this

The skill sequence shown above is based on ashe give that the enemy team has a [color=greenjungler[/color]. If you are not mid or if they do not have a jungler take volley and frost shot and when possible ult.

Passive - Ashe has this from Lvl 1, Increased chance to crit. How to use: When you get to your lane don't waste your first shot on a minion ever if you can help it, as your first shot will have %100 chance of crit. Instead run toward the enemy champ either zoning them or hitting them with your crit and volley. This combo should start them down a with a good chunk of life gone.

Frost Shot - Skill give the Perma-Slow affect. This will been the down fall of many champs because they just can't get out of range of your rain of arrows. How to use:This ability is toggle on off. Use this ability every time you attack an enemy champ, but never on minions as it would waste mana.

Volley - Great in team fights and around towers. It can hit multiple enemy champs with one click it also deals bonus dmg over your normal auto attack, and it slows too. How to use: Laneing, If you are running out of mana you are using this spell to much. It is best to try to grab two minions at once and to harass. When at attacking a tower or even defending it is usually a good idea to spam this spell and try to as much dmg to enemy champs with out taking any unnecessary dmg yourself. Use this spell when ever you can in team fights the bonus dmg will help take down who ever you are focusing. Make sure you have enough mana for your ult after lvl 6.

Hawk Shot - Ok this one is great for checking on the enemy jungle if your mid. If your not mid this skills is pretty much useless while laneing. It sends a hawk to an area revealing it temporally. It also give bonus gold on minion kills (very minor bonus gold and not why we take it). How to use: If the enemy has a jungler we can make some basic assumptions about when they will gank. They usually only gank after grabing both buffs. You can safely scout the blue buff a lvl 2 from the mid bush. By process of elimination it will tell you where they start. So you can find them with your next hawk. Once you get your second in hawk shot send it up to red buff or blue buff depending on which one should still be up. If either buff is sill up you and your team can safely push up in your lane with reasonable assurance that their jungler will be not about to gank. When both buffs are down you should announce that the jungler will be ganking soon.

Enchanted Crystal Arrow - Ashe is famous for this skill. Any ashe worth her salt better be able to land this skill shot and know WHEN to use it and WHEN NOT to use it. How to use: To make best use of this skill you first must be with in chasing range of the target. Shots across the map will rarley yeild positive resutlts. To many times this spell will make people over reach and the other team may benefit from their eagerness. This skill is a cheap shot used either in team fights for the aoe dmg and the stun, or it enables ashe to selectly target an isolated target. It works really well with pikcing off one person who is over extended. Ashe can do this by herself or with the aid of teamates, Ashe will need help if it is a tank or an off tank. Map awareness is imporant when try to pick some one off. If you are dieing because other champs come in while you are trying to pick some one off your doing it wrong. Only go for the pick when it is safe for you to go after them. Oh and don't miss. Additionaly this skill can help a team that has had trouble starting fights. Wait till their high value target (Ap burst or Phys Carry) amd they are close and fire it at them. This will help ensure that their carry dies in the battle.

I was really surprised when I did not see this exact build some where else on MOBA. It could be other their however this all came out of my mind.

Early game
go w/ the blade to start. If you are forced back consider picking up a second one. Otherwise don't leave mid unless you have to. I can usually at least complete my speed boots before I have a chance to make a quick trip back to the shop. A note on boots, berc greaves -- I prefer the speed boots because you will get out of jams and are more able to chase down feeling opponents. Attack speed on Ashe isn't helpful because it wastes mana in team fights slows, what I mean is that slows don't stack even if you hit the guy 25% more times that just a higher mana consumption.
Mid game
Finish inf edge, after you have edge done you can usually leave mid long enough to get a gank in another lane and get back w/o anything terrible happening to your tower. After finishing Inf edge start banshee veil. BV is the best survivability item out their right now for ashe bar none. Even when the other team is highly physical the passive on BV means that you will get out of more jams, it also has extra mana which is another big plus for ashe. Please pick this up before Phantom Dancer HP and the passive adds much more survivability than speed alone.

Late game
Phantom Dancer, Once you have this and speed boots even the fastest champs won't be able to catch you with the exception of possibly warwick(with blood lust) kassadin in a foot race. Also you crit a lot more and you will have a synergy with Inf Edge. It also means you can chase down anyone and can quickly dart in tower range to get a hit and get out before tower targets you. After that last whisper the armor pen will add more dmg than any other single item you could pick up at this point. Sell the blade and pick up bloodthirstier finally for the life steal.

Other items
Madreds BLood Razor -- Good proc but don't really need it on ashe and attack speed is what we are primarily after. Only reason you should buy this is if their is a flaw in the opposing teams build and many of their champs are stacking hp. Only then will it be worth it.
Witts End: attack speed and MR not really ashes thing.
PhiloStone/shurelya's reverie - I used this one for a long time builds a decent item only worth it if the other team has very little CC, You could take this instead of BV.
Brutilzer/yoymuu's Ghostblade- The brute is a decent item early game, i just feel its a little over priced for 25 dmg and some armor pen. It doesn't seem to do enough on its own in my taste. But it is viable and the CD cool down is nice too. Ghost blade Seems to synergies really well w/ inf edge I would upgrade to Ghostblade after build BV and after zeal.
Back Cleaver - Attack speed so we avoid it because of negative synergy with our frost shot.

Flash -- Great go to summoner spell for any one that needs an escape mechanism.
Ignite -- Works great for early ganks. Many combos of Crystal arrow flash and ignite will get kills.

Other spells

Ghost -- Great spell take in lieu of Flash same principle as flash. It is also acceptable to pair this with flash as well if you need the extra escape.

Heal -- Another good spell, Not great. Although it has almost unlimited utility. I used this spell a lot when i first started playing her. It can be used to draw the opponent out and you have a surprise extra several 100 hp. Or when you need to heal because you are going to die for another reason. I'd take a point in heal instead of greed if you use this one.

Teleport -- Works great with Ashe. Take instead of ignite. You can fire your crystal arrow in spawn and arrive just in time to make a kill.

Fortify - I always liked this one, but would never seriously consider it give better spells like ignite.

Exhaust -- I don't like this spell because I have to get close than my auto attack which is some times hard to do. And getting closer to the opponent is getting closer to danger.

All other summoner spells are pretty much useless on Ashe