When you'll have sona you have to farm in the early game in order to take levels and gold so you can start the building but you have not to use Hymn of valor on minions because you won't be able to get away in a fight no mana no kills more deaths


Early game
Sona is a difficult champion so you'll have to know when to struck Hymn of valor to kill enemies.If you want you can go mid to play her like mage also you won't try to take first blood if the enemies have 2 or more tanks and difficult mage or ad opponents

Mid game
In the mid game sona is half built you play more like a support you heal your allies you give them damage or movement speed so they can escape or attack with more damage or movement speed.

Late game
In the late game you have to play sona more like as a powerful mage than a support because your goal is to win so you active Crescendo in gang fights so you can help the others and yourself with Hymn of Valor to take kills for the team and for you