Build Guide by
Not Updated For Current Season
Go for Crit Chance, Atk Speed, Armor Pent, Ignite, Crit Dmg, Creep Dmg, and Havoc.
For Defensive Masteries, go 3 in MR, 3 in Armor and 3 in Dodge. Her passive + dodge chance rapes.
Typically, just start off with boots. Later upgrade them to Berserker's Greaves. Then you want to buy a B.F. Sword. If, for some reason, you cannot afford that at least get a Vampiric Scepeter. Updrade into the Bloodthirster. Do this 5 times. With Great Farming, you should have
550 Attack Damage and 125% Lifesteal.
Boomerang Blade is the first skill you want to max and the first one you want at level 1. After that, go for Ricochet and then one of the most useful skills, Spell Shield which I don't know why Sivir has. Of course, you want to get her Ult every time you can.
Personally, I take Ignite and Exhaust for the 1st Blood, but you can take anything else other than Clairvoyance, Heal, Revive and Fortify. Some of you might be wondering about Smite and Rally. Rally is good for teamfights as well as Turret destruction. Smite is wonderful when taking out Cannon Creeps.