I rarely see any Sivirs played in Dominion even though she is an amazing bottom. She has her counters like everyone but she is one of the best AD carrys bot.

Attack damage and Defense runes, pretty simple. The Movespeed Quints is what I like most though. It allows you to escape harass easier and sometimes saves your life when you get ganked or make a mistake. Even if you run a tiny bit faster than your pursuer that still means they cant catch you.

AD Masteries for an AD carry. You can of course switch some around if you have a few problems with some.

You may notice I don't have much attack speed items, that is because I feel her ultimate On The Hunt should be up every time you want to commit to kill your lane rival. You can always Boomerang Blade and Ricochet the creeps away easily, so its next to impossible to outpush Sivir thus giving you time to wait for its cooldown.

Sanguine Blade- This item will be your main sustain, and sustain is very important bottom because you usually deal with heavy harassers.

Black Cleaver- They will most likely try to counter you with armor especially if you are doing a real good job at harassing, and this is an amazing item vs armor.

Trinity Force- Best of all worlds, I usually grab Sheen first to proc on her Ricochet, then Zeal for the movespeed and attack speed, of course you can grab a Phage if you wish before Zeal but I always recommend getting the Sheen first.

Maw of Malmortius- Great item to get if you are versing a AP bot, go ahead and grab the Hexdrinker early if you are.

The Lightbringer- While a perfect counter to stealth characters it also gives good stats with a decent damage passive. If this isn't enough armor for you then grab a Thornmail or Atma's Impaler.

The skill sequence is pretty straight forward, you want to go for harass and damage first.

Boomerang Blade- Your bread and butter, allows you to outpush and outharass the enemy.

Ricochet- Even more push and harass potential, especially with Sheen.

Spell Shield- Use to block heavy damage or heavy CC moves, obviously.

On The Hunt- Activate whenever you seen an opening to kill your rival bottom. They usually don't anticipate the bum rush and massive damage.

Exhaust- Great for facing AD's bottom and stopping enemys from escaping your wrath.

Revive- Who doesn't use revive on dominion?

If you were looking to play Sivir on Dominion I am hoping this helped.