Let's break it down, Sona needs:
1- Mana
2-Ability power
3-Cooldown reduction
4-Help teammates

And this build covers it all in the finest way possible.

-Your first back should usually be after hitting level 4 (when you get your E).

-When the game begins, activate your Q once in the base, then activate again while helping the jungler, then when you go into the lane, your passive will be ready and your first poke will hurt a lot.

-if the enemy doesn't have a stun ability, play aggressive, but if they do, then try to play safe.

-Keep your eyes on your minions, and try to poke just when the enemy is trying to last hit a minion, and be extra aggressive when it's a cannon.

-if the enemy is focusing a lot on warding brushes, get the Sweeping Lens and Control ward on your first back and kill their wards to create pressure.