I ask above all else you be gentle as this is my play style and it works well for me.
This is my first guide, so it's still just a baby.
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Alright, so I fell in love with Sona when she was introduced. Before Sona, I dedicated my time to Janna and Soraka. But then Sona showed up, and I was head over heels in love with her unique play style. I've played her since then, and have endured all of her nerfs. I've found that this build has to be one of the most solid, as it helps you deal with her more recent nerfs (q, and lack of innervating locket)

Buffs

Golem - Now highly recommended for Sona. This allows you to cycle through all of your auras, and constantly use your W to your team's benefit. Try to get your team to assist you in getting this buff or if you're aware of where everyone is, pick it up yourself.
Lizard - Pretty useless. While you can use your Q to slow an enemy that is running away, it benefits others much more.


Item Selection:

Let me explain why I choose the items I do. Rod of the Ages for the AP that slowly snowballs. It's useless to pick up late game but a great item early game to obtain now. It makes that Q nerf not sting as much as it did and benefits your W with an extra boost from AP.

I generally pick up Boots of Mobility to allow me to get across the map quickly if I'm not in a team fight. It also allows me to support from the back and sides through walls if needed. When there is high CC, I opt for Mercury Treads instead.

Next, I obtain my CDR items, that usually top me out at 40% easily. This allows my team to depend on my healing in team fights and the On-Use passive from Shurelya's can allow me to initiate with my stun and get out quickly.

Lastly I get my Archangel's Staff and then either Frozen Heart or Aegis depending on their team composition.

Set-Up for Sona:
For Summoner spells I select Clarity and Flash. Flash for the clutch escape or to set-up a gank and Clarity for caster support and lane longevity. I try to stay as long as I can to purchase Rod of Ages before the 20 min mark.

Early Game:

With the lack of locket, I skip the mana manipulator for now. I pick up a Sapphire Crystal and 2 HP Pots. Use the pots to supplement your healing. As soon as you can, recall and pick up your Catalyst. By this point, your Clarity and Catalyst with Awareness from the Utility tree make it hard for you to be forced to return to base.

Just use Q to last hit and possibly harass your enemies in lane. Remember to Power Cord enemies and use the bushes to your advantage without overextending.

By this point you should have your parts for your Rod, and your basic boots of speed if you have not killed anyone in lane. If you have, you should have your Rod by the 15 minute mark and starting to build your boots.

Mid Game:

By this point, as the support you should be working towards your items but also purchasing wards and placing them in the normal strategic locations.
I find that as a support, this is your duty. While it's nice to have help from others on your team, this is by far the best support you can give -- knowledge of where the enemy is.

You should be helping to push towers and lanes forward, and possibly baiting as for some reason Sona looks yummy to unsuspecting carries who end up dead instead. Try to not hang back too far behind or too far off on the side. Time your Ult to counter other champions, especially taunting tanks. Use your Powercord on targeted enemy carries.

Late Game:

Most of your items are built, and you might be subbing in others like Mejai's Soulstealer or even Zhonya's Ring if it's gotten that far. You can start buying Elixirs of Fortitude or even Brilliance if your set is complete. Don't get cocky though and stay with your group. Continue to get Golem if you can and time your skills. Never spam, it doesn't benefit anyone. It's like overhealing in WoW, it's wasted mana.

I hope this helps out any aspiring Sonas. Thank you! c: