Lethal Tempo is the main rune for Sivir since you will need the attack speed to do more dps and put your W out faster.

Presence of Mind helps us spam Q more since it regenerates our mana, we can also take Triumph if you know how to manage your mana.

Legend: Alacrity Is a great rune to add to Lethal Tempo and give out more attack speed mid/late game, Legend: Bloodline is also a great rune for more sustain.

Coup de Grace gives us more damage to do when enemies are on low health this can help do more damage to tanks and make sure to let us win 1v1's.

Celerity is a great rune since it gives us more speed with our passive and ultimate, we used to take Nimbus Cloak but it has been nerfed and is underperforming so celerity is the better option here.

Gathering Storm is a great rune to increase our dps late game and deal out more damage in teamfights.

Kraken Slayer is a good mythic for Sivir because she can deal quite some damage with it, you usually use this against tanks since this item gives you bonus true damage every third auto.

Immortal Shieldbow is probably the best mythic on Sivir, take this mythic if there is burst champions against you like, Zed, Talon, Draven, Master Yi, Rengar and Kha'Zix.

Berserker's Greaves is the basic boots for ADC's since it gives us more attack speed.

Essence Reaver is Sivir's core item which was recently buffed, it gives her more ability haste and restores mana, this item also gives you more damage the next attack you use after an ability.

Infinity Edge is the 3rd item for Sivir since the passive works at 60% crit, it amplifies your crit to do more damage which is one of the core item's for any crit ADC.

Phantom Dancer is basically a attack speed boost, after 5 attacks in a row you will have max stacks and have increased attack speed on each stack of phantom dancer, this will increase your dps output.

The Collector is a great item for ADC's this season since it provides you with crit and lethality its passive that executes champions under 5% which is great against tanks.

Lord Dominik's Regards is a really good item against tanks since it does max health damage against enemies and gives you armour penetration to do more damage.

Bloodthirster is an item if you need more sustain, if you cant win fights or you are being outdamaged.

Mortal Reminder makes sure you remove healing against enemies such as Soraka, Yone, Yasuo, Vladimir, Samira and Aatrox.

Guardian Angel is an item you usually shouldn't resort to since it doesnt give the last 20% crit, take this only if Immortal shieldbow isn't enough and you are still getting oneshot, Usually take this when you have a Veigar against you.

With CRIT Sivir your early game is all about poking and pushing the wave this will provide easy drakes, make sure to not push too much or you will be an easy gank target.

Make sure to use your E more often, especially in laning phase where your mana is needed most, you get mana back if you block something with your E, best example is a Caitlyn just walk into her traps with your E to keep your mana up.

With crit Sivir's main damage source is her W in team fights since you are able to burst out damage to multiple targets at once, also if your first initial attack is a Crit all other bouncing attacks from your W are guaranteed crit as well.

Make sure to not really be the first to engage since you have less range than other adc's so you cant be auto attacking people randomly, make sure to stay in back line, ult and start auto attacking the tank with your W to spread out the damage.

Remember you are a utility based ADC you provide help for your team, you dont do as much burst or damage, but you provide speed boosts and great dps to the entire enemy team.