Start with Prospectors Ring, Boots of Speed and one of each potion Upon your first visit back buy your Sorcerer's Shoes .
Then, to quickly start packing a punch buy a Haunting Guise and work towards completing your Blackfire Torch . Don't worry about the gold per 5 from Kage's Lucky Pick as it is not very important in Dominion. Once you have rushed a Blackfire Torch your spells will start hitting hard enough to gain some kills and keep your teammates in battle.
Continue the core build by purchasing a sheen followed by your best friend Mr. Nuke… the Lich Bane . The Sheen is an early statement to the destruction you can cause, once you follow up with a Lich bane mosts enemies (excluding anyone stacking MR) are sent running after a short burst + auto-attack.
Before asking negative questions concerning this core build, follow me here for a sec. Consider this! Sona has a passive that stacks extremely well with the lich bane. not only that but around midlate game you can nuke just as well as great ap bursts like Leblanc and Ryse or Ziggs all while healing your allies and helping them get away and catch up to and from battle.