Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Sona is a squisy character with low mana at the beginning. However, she's an awesome support if you play it right. With Aria of Perseverance and Song of Celerity, your teammates are at an advantage against others. NOTE: Sona is a support character, therefore it will make a good team into a GREAT team. However, if your teammates are not good then you can't really carry your team.
Focus on last hitting creeps whenever possible since Sona is not good at farming creeps. Try to conserve mana until you get Tear of the Goddess then mana shouldn't be a problem. Use Clairvoyance to help prevent ganks.
Pay close attention to map and be aware of your surroundings. Help your teammates chase or run away whenever possible by using Song of Celerity and Crescendo.
At this time of the game you should be able to keep all 3 buffs on your teammates. Stick together and don't charge into the battle first. Then it's GG!
Choose different boots depending on enemy composition. Since Sona is hard to farm creeps with low mana at the beginning, you might want to get Philosopher's Stone at the beginning.
Sona is a wonderful champion to play with. You won't get too many kills but you will enjoy saving your teammates in crucial moments. Have fun and goooood luck!!