The Sivir buff has turned this laughed at hero into a turret pushing backdoor queen. The only place she should ever be during a 5v5 is running middle lane, 3v3 it depends on your opponents' selection: without assassins like teemo, twitch, xin etc., or the ever infamous tryn, she can manage top on her own without problems.

Lastly, I will say don't expect to go positive unless you have great support from your team, and moronic enemies. Sivir has little to no escapability. However, your opponents won't know where you'll be coming from until a turret drops, and in 5v5 games it will be your job to make sure whoever the opponents send mid-lane can't get gold off minions, while you make it rain gold pieces.

More often than not my victories have been with our team down on kills (eg. 20/30) myself being a main contributor (usually 2/6/3 by mid game) but dropping 5 turrets and an inhibitor by 18 minute mark, without having lost a single turret, usually is enough to seal your eventual victory.

Armor Penetration and/or Attack Damage are your best friend, I prefer Arm Pen.

Spell Shield gives you the ability to take most casters, but AD speed strikers shred Sivir with little to no resistance. Dodge has saved my life on more occasions than I can count, and most heroes will overextend for the kill, and a lucky dodge can seal the enemies' demise without the reward of your dead body.

As far as glyphs go, I'm sure something better than MR can be used, but that's my own preference. Spell Shield will help a lot, but I'll take the small amount of MR from runes over using an item slot for MR that won't keep you alive anyway (I repeat Sivir cannot take a hit)

Most people will think I'm high for this, but Sivir is not a hero for team battles. She specializes in 1v1 and pushing minions.

The most important masteries are the minion damage reduction/extra damage, siege commander, and demolitionist.

Siege Commander + Demolitionist combined with Sivir's Ult makes her a turret danger at level 6

The most important ability Sivir has is her Boomerang. With is scaling with AD finishing your Manamune as quick as possible makes her a force to be reckoned with. The reason for the Manamune priority over say a BF Sword, is that Boomerang Blade is very expensive in mana. Especially if you expect to harass the opponent and kill minions with it.

Depending on your laning opponent you may want Ricochet at lvl 4. More often than not however, lvls 2 and 4 should be spell shield. This is Sivir's bread and butter, and can make or break how successful she is.
Skill shots, especially, can even put priority to level your spell shield over your boomerang blade!
There is nothing better than spending 75 mana, jumping in front of Nidalee's Javalin or onto Swain's Nevermore only to recieve 150 mana and laugh as your opponent just wasted mana and put their best ability on cooldown. Snares such as Morgana's skill shot, and Swain's Nevermore can really surprise your opponent as they push forward to take advantage of your condition, only to find you are undamaged, unsnared, and revitalized with mana.
Always keep a look out for Ashe's Ult, you can really save a teammate's life by leaping in the way, and activating spell shield.

Lastly is Ricochet. After finishing Manamune, and then building your first BF Sword you'll have the damage output to wipe a whole wave of minions with a single Boomerang Blade, with a follow-up Ricochet Shot. If done correctly you won't even break stride as you push down a lane running at full speed. As you approach the tower the enemy won't have had enough time to be there waiting, so activating On the Hunt, all the minions you have in your wake will spill over the turret like a tsunami all having significantly increased attack speed with your own damage to couple theirs. The turret will drop fast, and then you bolt like a bat out of hell before the enemy team's fury can be brought down on you.

Sivir's ability to push lanes at high speeds makes travel spells like ghost and teleport even more dangerous. Say you push top lane and destroy the second turret, hop in the bush and teleport to bottom lane, while the enemy team is scrambling to right the wrong that has happened, you have now pushed a second lane to another turret.

Ghost, while being your only escape when coupled with Spell Shield, and the movement increase from On the Hunt if need be, can easily allow you to jump from mid to an outside lane.

If you'd prefer flash, I'd suggest keeping teleport, as it is great for farming mobs that have formed in the absence of a pushing hero, in addition to the above strategy.