In lane Q whenever you can. It’s usually not worth to take anything in return though and especially not CC, even moreso CC in range of their adc. Don't W much early or you'll go oom; preferably W for the shield, not just the heal. Use potions instead if chunked. You can roam if clearly necessary, like for a herald fight, but you don't get much out of random roams. You win by default, so the onus is on the enemy team to do something, so focus more on not dying to their plays than doing anything yourself.

After laning, try to stay with teammates so that you don't get caught alone and die for free, and you can peel teammates. If you're with a strong teammate you can often ult anyone as soon as they come in your ult range. Extended deathball fights are good - you get a lot of value out of auras and sustained healing, so for instance if you get a random kill you can often start baron and stay full hp.

Passive chords: W most often in fights, especially when enemies dive; Q for poke (mostly in lane) if they aren't fighting back; E to chase/kite. Passive is an auto reset. With 3 stacks and q/w/e up you can use a power chord then quickly rotate abilities for another chord for combos like slowing twice (the possibilities are endless…if by endless you mean 9).

Standard enchanter items/runes are usually good and Sona gets a lot out of their ap, cdr, heal/shield power, and mana/mana regen, and applies effects from items like staff of flowing water to many teammates repeatedly. Although Sona is known for scaling, benefiting a lot from items means you snowball surprisingly well - winning lane gives you an early 1 or 2 item spike. The minutiae of different builds don't matter nearly as much as playing well; just copy the few highest Sona players and focus more on playing better than building differently.

Review:

1 your deaths

2 what happened before your deaths (eg bad trade)

3 times you could Q/R more aggressively, or conditions that should lead you to position more or less aggressively

That's it! glhf