Hi there, this' my first guide, old gamer, used to play Dota since before it was known as Dota, and many other games like Ultima Online, Warcraft3, WoW, etc. I'm not the best at ranked because my time is limited, so take this guide with a grain of salt. This guide shows my personal preference in playing this champion and you should see for yourself and adapt as needed.

I used this build to get to Mastery Rank 7, keep that in mind.

Not gonna overextended, I just want to explain how I ended up with this build of one of my favorite characters that I've learned to love.

1. Sivir is a late game champion: Like many champs, Sivir is very squishy in the early game and you don't have any means of escape, so you gotta be VERY careful and I advice against getting into a fight unless you are CERTAIN that you'll survive. In the late-game, Sivir becomes an INSANE killing machine, clearing waves like no other champion. Only the likes of Ryze can get close to her but she's still better than that.
So play to that, focus on surviving, farming and defend your base!

2. Sivir can be played top: well, sometimes. The fact is, Sivir hits like a truck early so you can really punish some of the strongest Tops. I'm talking about guys like Mordekaiser, Nasus, Renekton and most of the "tough guys" that are commonly seen in that lane. Every time they go finish a mob, you punish them by getting your hits in. Very soon they'll have to head back to base or risk getting killed. Obviously you need to have a very well positioned ward or you'll get ganked hard.
DONT BE AFFRAID to use your Blink or R as soon as you see them trying to reach you, or it'll just be too late.

3. Most Supports have no idea how to play with you: Since you got almost no way to survive, and most Support like to play aggressive, they might think you'll put yourself at risk as well. This is no good unless you're well positioned to do so. You'll end up dead easily, and I prefer to stay alive. Talk to your support and play calm, the focus is on farming and staying alive. Besides, you'll be helping your JG get better ganks if you let them push your lane.
Its not that you can't play aggressive. YOU CAN, but first make sure that your support knows what he's doing.

4. Know how to use your spells/abilities:

-Use Q to hit both the enemy champions and lane doods that are about to die.
-Use W only after an autoattack, since it resets your timer you'll perform a double attack, this is primordial to your burst and one of the reasons why Sivir hits so hard.
-Always try to intercept spells in the early game with E, it'll give you mana to stay in lane to farm and you can also help your Sup survive by doing so. Sivir has very expensive spells so I always choose that ability on lvl 2 with very few exceptions.

5. Why Exhaust / Stormrazor: Sivir doesn't have any slows, stuns, dashes or anything like that. For that reason I ended up playing these pair since they give you more ways to control opponents and survive. Stormrazor is very good because it goes in line with what you're commonly building for, which is Critical Strike.

6. Positioning: Sivir works best from behind the team, you can force fights with your R but remember to always stay behind your buddies. A living Sivir can turn games around even when all your inhibitors are down.

Well thats about it, I hope you can get something out if this if the other guides didn't get there.