Sona, one of the most underestimated champions, is capable of terrible, terrible things. Her burst damage is huge, her ranges are disturbing, and her overall utility is amazing. This build is meant to turn Sona into a laning machine. You'll never have to leave your lane and your team will enjoy your presence through the thickest and most brutal of team fights and ganks.

Note that Sona's newly buffed passive increases her utility by amping up her Power Chord. Slow enemies down, reduce their attack damage, nuke them, rinse wash and repeat.

I typically go with a fine mixture of Magic Penetration and Ability Power. Given that Sona's incredibly powerful attacks are using Ability Power, it's probably a good idea to stay boosting these two stats. I keep more of an emphasis on AP, however, as her heal benefits from it. Some go for Mana to pump up the Archangel Staff, but quite frankly, Sona's mana problems will dissipate quickly.

As far as masteries, I go with the standard mage-bomb's 9/0/21. I see a lot of people not capping out Expanded Mind, but I think the extra 5% mana just helps the early game and Archangel's Staff that much more.

For summoner spells I absolutely love Clarity. Again, the purpose of this build and ultimately Sona is to stay with her team and lend her epic support. Clarity will keep you in this position early game and throughout the game. I take Flash as well because I believe it's important to have an escape mechanic with Sona. Frankly, players will often try to gank you (you are supposed to be a weak little cleric after all). To avoid spending time out of the game I take Flash. Exhaust and Ghost are good alternatives, so it'll just be a matter of preference.

One thing I'd like to note is that this item build is meant to be very flexible depending on the matchup. For instance, in 3v3s and in 5v5s where my lane is being handled well I often will take Catalyst and Rod of Ages before completing my Boots of Swiftness. If my opponents are playing tanky, I'll go for Deathfire Grasp. If my opponents are ignoring Magic Resistance, I'll definitely take the Lich Bane sooner.

Here's my reasoning for taking those items in whichever order they come in:

• Boots of Swiftness: Make you very fast all the time. Combined with Song of Celerity, Sona is able to escape battle easily, run to support teammates quickly, and generally provide support in a hasty manner.
• Rod of Ages: A staple for mages, this item gives great AP, mana, and health. This item will for sure keep Sona in the battle for a very, very long time to maximize her support capability
• Archangel's Staff: Early in the game, Tears of the Goddess will cure your mana woes. Then, when it's converted to Archangel's, you get a major AP boost and your huge mana pool is becoming even more AP. Feels good man.
• Deathfire Grasp: This gives Sona all the cooldown she needs to allow her to triple aura and get her ult up in a (relatively) timely manner. Best of all it also gives her major AP and a wicked awesome active that gives her another bomb. Her offensive capabilities are dramatically increased
• Zhonya's Hourglass: Survivability, survivability, survivability. Combined with substantial AP boost of 100, Zhonya's armor boost and active ability will ensure that your late-game Sona will refuse to take the final bow.
  
  Some items to consider as alternatives depending on the matchup should be Rabaddon's Deathcap, Abyssal Scepter, Mejai's Soulstealer, and Frozen Heart. If paired against people with low magic resist, try taking Rabaddon's instead of Zhonya's for your late game item. If the opposing team is taking too much magic resistance and your team is heavy AP, try helping them out with Abyssal Scepter. If you are straight up owning the game and racking up assists (as you very well should), take that Mejai's before the Rod of Ages or Archangel Staff. Finally, if you feel that you need to bulk up a little bit, take Frozen Heart (this combined with Zhonya's should make you pretty tough).

Objectives of early game:

• STAY ALIVE! Sona is fairly vulnerable at the beginning and her getting killed too much can cost a lane, gold to correct her flaws, and general frustration. Conserve mana, use your heal, and generally don't get too aggressive.
• GET GOLD! Tears of the Goddess and Catalyst aren't cheap, but you're sure as hell going to need them. Get your last hits down!
• COMMUNICATE! Always communicate with your partner. You are supporting them after all. Also, you will need to be making trips back to shop, so make sure to keep your partner informed!

Midgame:

• SUPPORT! Now you can truly begin supporting your team in the fights that will begin to erupt. If your lanes are remaining stable, you can alternatively continue laning with your partner to really create a fine push.
• SUPRISE! With Rod of Ages developed and more AP boosters coming down the pipe, people will begin trying to pick fights with you. Shoot them in the face with your Hymns of Valor Power Chord to give them a what-for! Also, use your ult and Song of Celerity Power Chord to disrupt and slow opponents, assisting your partner(s) in slaughtering the enemy.

Late game:

• PULVERIZE! By now your AP is getting rather huge. Keep up the Hymns of Valor and deal solid burst damage.
• ORCHESTRATE! Make team fights turn in your favor by triple aura-ing, buffing teammates, healing, and debuffing enemies. Your ult is the ultimate disrupt in team fights. Hit as many enemies as you can and watch your team mop up.
• BE THE FINAL BOSS! The other team will begin to wither as you wreck their ability to team fight. Shift momentum with your buff spam. Most of all: Absolutely refuse to die! YOU ARE THE FINAL BOSS, YOUR MIDBOSSES (partners) NEED YOU THERE!