Sona is a highly valuable support champion, she uses her auras to help teammates by giving them movement speed, heals, Attack damage/Abililty power and her ultimate can stun an entire team if placed correctly.

If you are on the purple side then just do the same warding only reversed.

As for the choices i have for masteries i have a little problem with the new system but i focus mainly on utility as any other support, i go full on gold per. 5 and full on starting gold as this gives me an advantage on warding and i can hold lane longer.

The items are mainly support based, i start out with a Faerie Charm as this gives a good mana regen at start, then i build it up to Philosopher stone as soon as i have enough gold, from there i get boots and some new wards (always have ward by dragon early so the jungler can call when you shall get it). i then get Heart of gold as this gives even more gold, from there i complete Ionian Boots of Lucidity. As middle game approaches i pick up Aegis of legion as this gives my team an advantage.

The summoner spells are standard support spells