This is my First Guide!
I include this section so you guys know. I have no experience with making guides, so don't expect me to make this perfect.

Good Question! That mana potion in my first build is there for a simple reason. It lets you waste mana and still get a nice kill at 6. I know some of you veteran players are thinking, "Only noobs can't control their mana." That's fine, I get that. But I play pretty aggressively, and that means spamming volley every time it comes up. That eats through the old mana bar. So, why do it? Because it gives you damage. Think about it, if you're constantly harassing the enemy with volley, they should get hit every now and then. So, that gets them hurt, especially at the lower levels, where everyone has very little health. And that leads into the next item. Generally, you end up farming until at least, or past, level 6. So when you hit level 6, you have your ultimate. It's nice, does some damage, and gives a stun. But you're out of mana, and can't use it! Just use that mana potion, use your ult, and get an easy kill. Your volley should have harassed them down to half health, easily, the arrow gets them to 1/4, and you shoot them to end their life. Easy.
What if they "b" to get more health before level 6?
They can't farm from the base. You're now outfarming them, outgolding them, and outleveling them. You should be able to win. So that's why I have the mana potion.
If you've got Soraka, you don't need the potion, she just gives you some mana. Ignore this.

This is just a preference. I enjoy having Static Shiv because it helps me get some extra damage in the first hit, or when chasing, and that's nice. If, however, you are not a fan of Static Shiv, feel free to swap it with something else. The most popular choice to go in the slot is either another Bloodthirster, or a Phantom Dancer, if you haven't replaced boots, yet.

This is Ashe. Use your Volley when it comes up, and keep Frost Arrow against other champions. Arrow to chase down enemies, or right before initiation. Can you remember all that?

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As you can see from the screencaps above, I used my Hawkshot in certain situations, and the devastating results are all too clear.
Now that I've finished trolling you with non-existent screencaps, let's review when to use Hawkshot. Use it to scout out bushes, Baron, or before teamfights. When using it in teamfights, it helps because it prevents them from getting outside of your vision if your team retreats a little. Also, you can use it when coming back from base, if they're attacking your tower. Throw it as far away from them as you can, while still having it in their sights. They'll have no way of knowing how close you are, and they may run off, rather than risk a gank.

This is very much a work in progress!
I will modify things based off the comments, and add more sections for requests. So please, request a section that I missed, I'll be all to happy to add it.
THANS Damn it, I'm a busy man, I don't have time to make you a rainbow.
Thanks for reading. Happy?