Ashe is an early-mid game Attack Damage Carry which specializes in crowd control. In order to be a good Ashe player you must keep in mind that you are very immobile, selfless, and team reliant if you want to win the game. "Team reliant you say?" Yes. This is because of how immobile you are and the fact that your only 1v1 enabling skill is your ultimate, which should rather be used for getting picks on the enemy team so you can group on an objective with a numbers advantage. Now that that's out the way, I shall now attempt to impart my Ashe Diamond-ish wisdom on you.

In this guide I show some pretty standard all-in oriented ADC runes. These will work for you if you are unsure of what your rune preferences are.
-Armor and magic resist for trading well.
-Attack damage and attack speed for killing well.

Also, pretty sure the flat AD is taken into consideration when calculating Ashe's frost-applied damage. So there's that, too.

DISCLAIMER: Do not blame runes if you're dying 10+ times a game. :)

Heal
and
Flash
always.

Heal allows you to help teammates and give you a little extra boost in movement speed if necessary.

Flash allows you re-position instantaneously. Too good to pass up on most champions, including Ashe.

Barrier if your support is running Heal.

If you needed cleanse it's likely you screwed up elsewhere. Most times, if you're caught in an unfavorable position as Ashe you're dead anyway. Maybe vs. Twisted Fate. But then we still have Mercurial's Scimitar.

Ghost will make you depressed because it makes what little flashy play potential you had disappear with the absence of Heal's particle effects. Only mentioning because I've known people to run it.

Pros
-Highest kiting potential in the game
-Very high early-mid game damage due to passive
-Huge amounts of innate crowd control; still useful if behind
-Pick potential with ultimate

Cons
-No mobility in kit
-Damage falls off a bit late game
-Cannot hard carry if team severely behind

The only time you will want to be by yourself playing Ashe is to farm/shove out a lane. If you have no vision of an enemy that can potentially kill you do not shove further without someone to babysit you. Once you're done with that, you'll be looking for picks using your ultimate and grouping for objectives.

Get the red buff when you can. Some might say you don't need it due to your frost. I say they need to back the hell off of YOUR red, because YOU'RE still an ADC and red buff allows you to secure kills and enhance your slow even further to kite and prevent the enemy from escaping.

...If they're playing someone like Master Yi and seem like a decent enough person let them have it.

This is where you shine. The enemy wants you dead. They see how immobile you are and they see you have a lot of damage per second items built. This is where you deny them and make them regret jumping into the backline of your team because they will not be leaving.

You will kite them, ser or lady or whatever you wish your title be. You will flash what needs to be flashed and heal when you need to heal. And you will kill them. Why? Because you are Ashe. If they miss their gap closing opportunity to catch you, then they are nothing but damage for the end-of-game chart to show off to your team.

I will not go in-depth on orb walking (I'm sure there are YouTube videos out there), but kiting is the art of killing while moving away to avoid their clutches. Ashe makes this especially easy because she applies a slow on the enemy while doing so. This is your forte. Stay far enough out of the fight while using your W and AA as often as possible that they're forced to use their gap closer in a desperate attempt to catch you, and deny them.

If you deem there not a chance in the world you can kite the enemy during team fights to avoid a large portion of their damage, build defensive items.

Look into your offensive I-only-want-to-more-damage soul and ask yourself if it's worth it. Because it is.
Because if you take her damage to the face your team didn't have to in that instant.
Because if you lived she isn't an Assassin.
And she will be squishy if she calls herself one.

***
I have no advice for Master Yi. Build Guardian Angel and pray the Angel's cooldown will be lower for the next encounter.

While farming try to keep up your Q stacks in order to trade more favorable.

Also, avoid W the wave unless you want to shove it. It's a good poking tool, but if you shove the wave doing so it'll only making it more dangerous for you to farm. Which is unfavorable given what little escape options you have.