Sivir

Strengths

Sivir's Boomerang Blade returns to her after reaching the max range, so you can shift position to hit enemies who would otherwise have evaded it.
Ricochet resets Sivir's basic attack timer on activation, so activating this immediately after landing a normal basic attack will maximize damage output.
Try saving Spell Shield for enemy abilities that can disable you such as stuns and roots.

Passive · Fleet of Foot — Sivir gains a short burst of Move Speed when she attacks an enemy champion.
Q · Boomerang Blade — Sivir hurls her crossblade like a boomerang, dealing damage each way.
W · Ricochet — Sivir's next few basic attacks gain additional attack speed and bounce to nearby targets, dealing reduced damage while bouncing.
E · Spell Shield — Creates a magical barrier that blocks a single enemy ability cast on Sivir. She receives health and a burst of movement speed if a spell is blocked.
Ultimate · On The Hunt — Sivir leads her allies in battle, granting them a surge of Move Speed for a period of time. In addition, Sivir's attacks reduce her spell cooldowns.

A suggested 5-lane lineup built around Sivir, based on hero partnerships and role synergy — not win rate.