Feel confident. Playing Sona will usually turn out ok as long as you do not misuse her passive and aren't fighting some of the strong threats on the chart. Remember to mainly go for your Q passive.

If you see an opportune moment to roam especially to the bot lane take it. Don't be afraid to steal kills unless the ADC really needs them because he is behind. Your team should be great full to the tremendous amounts of damage that you deal.

If your getting camped or getting beaten in lane just wait for a gank. If not just play safe. Assassins usually counter Sona unless they are bad players. A BIG threat to any AP champ even Sona and how strong she is. is magic resist. This is also why I personally don't play her in ranked. People are usually smarter and get like two MR items and your done.

Sona cannot fight 5 people at once. This should be obvious. The only way your getting a pentakill is knocking em out one by one.