Is a monster when it comes to wave clear and AOE damage with her Ricochet ability. She can also provide utility with her ultimate On the hunt ability which provides movement speed.

Pros
+ High Damage Output
+ On the hunt allows for high utility
+ Ricochet Allows for high damage output and amazing wave clear

Sivir is able to make game breaking plays when it comes to engaging or help engaging with your ultimate. You also counter sieges with your Ricochet. She has the best wave clear out of all of the ADC's. She also is rather safe with her Spell shield ability.


Cons
- Unsafe with On the hunt on cooldown
- Has a hard time coming back if behind
- High mana costs

Sivir is rather easy to beat in a 1v1 early game. She is also defenseless when her Spell shield is down. Doesn't have a level 6 power spike in lane, ult is only practical in team-fighting. Overall weak early game and is reliant on critical strikes.

Passive Fleet of foot gains movement speed whenever damaging an enemy champion with an ability or a basic attack. This is good as if you had Fleet footwork though you don't really notice it that often. You don't really notice this passive, and it doesn't really do much, it is more of like a niche touch.


Q Boomerang Blade This ability is the ability you want to max first, as it provides for good poking damage in lane, and can clear waves rather fast along with your W, Ricochet. This ability is a long range skill shot that does damage on its way to max range and back. Though this ability doesn't really do much damage later on in the game, it is good to use it in between your autos or when you are out of reach to get chip damage off. You can also use this ability to farm from a range in lane, if you are not able to reach the minions.
THIS ABILITY SCALES IN AP AND AD


W Ricochet is your bread and butter of the kit. This is almost the only reason why you play Sivir other than the fact that your ultimate provides a lot of utility for the team. You can use this ability to basic attack reset after a regular basic attack. You want to max this ability second for maximum damage output. Whenever you auto attack and it crits, all following ricochet hits will also crit.
THIS ABILITY SCALES IN PHYSICAL DAMAGE


E Spell Shield This ability is what you want to max last because this ability provides no damage. When used you gain a shield that will block a spell and your shield lasts 1.5 seconds. Whenever you upgrade this ability you only gain more mana and lower the cooldown which is what you don't really want. That doesn't mean this ability isn't useful it just means that you would rather have more efficient upgrades. You want to save this ability for when you can absolutely not dodge a cc or important spell. Unless you are desperate for mana or need mana, don't use this ability for random spells like an Ezreal Q.


R On the hunt is the ability along with Ricochet that makes Sivir a late game monster. You want to use this ability when you need to chase down enemies or escape. That is the simple use of this ability. This ability could be the edge you need to win a team fight, because movement speed can be the deciding factor between making important catches, or being able to escape and reset for another fight. Movement speed can also give you the ability to dodge skill shots or force a fight that favors your team. There is also a unique passive that gives you % bonus attack speed while Ricochet is active. Upgrading your ultimate buffs your attack speed bonus, movement speed, and movement speed duration.

You want to use fleet footwork because it is the most balanced for ADC's. It provides healing and movement speed. You also want to use triumph grants you additional gold on takedowns, and it grants you 12% of your missing health, which is good because a lot of times in the bot lane, since it is a 2v2 lane, once you get a kill that hp you gain back could make or break you getting a double kill or dying. is good because as Sivir I believe you lack base attack speed so this rune can help you with that, and helps with last hitting. Coup de grace is good for getting that final hit on somebody when you need the kill since you deal extra damage when the enemy is low.

When it comes to teamfighting as Sivir I don't really think there is much to do, as you are a backline powerhouse after using your ultimate On the hunt, you start to use your W Ricochet and you start to auto and damage everybody with your critical strikes. Remember to keep an eye on yourself though to be ready to use your E Spell shield. You also need to throw Q's in for maximum damage output when you are out of range or in between your autos.

I hope this guide helps you!