Choose Sona againts a lane that suffers from hard poke. Ex. Taric, Alistar, Blitzcrank, Leona, Braum. Just be careful not to get all inned/pulled unless you're facing Taric (Probably your best match up).

You can also choose to go 0/21/9 if you want to be tanky. Otherwise choose this.

You can also choose to go AD marks if you're planning to auto harass a lot. Hybrid penetration marks can also be used instead of magic penetration marks.

Usually take Exhaust and Flash. Ignite can be taken if you want more kill pressure and they have no one to pop your adc in teamfights. Take heal if your adc decides to go barrier.

At level 3 you can choose to get a second level in q if you aren't being pressured in lane. Max for poke/sustain and get ult at the normal levels 6/11/16.

Starting Buy:
Start spellthiefs with pots and/or wards. Trinket is up to you, usually the totem but you can choose the lens if you're feeling lane dominant/ambitious.
First Back:
If you have enough gold for the sightstone, get it over the frostfang. If you have enough for both, then get both. Once you have the sightstone, swap out your totem (if you have it) for a lens. If you do not end up purchasing the sightstone, grab some wards. Buy pots if needed. Buy pink ward if you want more dominant vision/dragon control.
Future Buys:
Grail is a reliable mana item for lane, or get the idol if you cannot afford the grail. Get boots at some point as well. Glacial shroud is a situational over idol/grail. More pinks are always good.
Full Build:
Usually take ionian boots over mobi if you have 5% more cdr in your runes/masteries.
Situational Items:
All items very upon situation but can still be very strong on Sona.

Against all inners, try to dodge their engages or force their engages when you know you can win the trade. When they miss their engages, take advantage and put pressure on the lane by zoning/poking. When making trades, q first and then w if they retaliate so you can mitigate damage (w shield has a short duration). Also try to tag your adc with your auras in 2 on 2 trades. Trade when your power chord has 2 stacks so that you can power chord immediately during the trade after using a q.

Peel/catch people out with your powerchord slow. This becomes even easier when you get iceborn gauntlet. Do not always go out of your way to tag your teammates with your auras if your positioning suffers from it. Otherwise, make full use of your auras and help your team as much as possible by shielding, doing damage, speeding up, slowing, and obviously using your crescendo (hopefully on multiple people, but does not always have to be depending on the situation). When pushing turrets, make use of your powerchord!