Secret Stash- Your potions/Elixirs last 10% longer. These biscuits restore 15 HP and mana instantly
Merciless (5 Points)- Deal 3% increased Damage to champions below 40% health
Dangerous Game- Champions kills and assists restore %5 of your missing health and mana
Precision (5 Points)- Gain 6 lethality and 1.5+.25 per level Magic Penetration
Thunderlord's Decree- Every 3rd attack against one enemy deals a lightning strike and magic damage in the area. 10 Damage per level, plus 30% of your bonus attack damage, and 10% of your Ability Power (25-15 second cooldown)
** I use this even as a support, I have tried windspeakers on her, but thunderlords just feels better
Power Chord- Every 3rd spell Sona gets bonus magic damage. make sure if you can to auto auto Q so you get your power chord available. This does crazy damage. In late game I can almost wipe out an ADC like MF or Jinx with just my Q and Power Chord
Q (Hymn of Valor)- This build gives Sona ridiculous damage, so I like to max this out first. Remember when you are tower hitting to use Q to give extra damage. Also use Q if you have mana on Dragon and Baron so that your teammates get the boosted damage for 3 seconds.
W (Aria of Perseverance)- I max this out second. This heals the most wounded ally near you and grants a shield for 3 seconds to Sona and an ally
E (Song of Celerity)- Do not unlock this until level 7. I never have use for this until then. It is the last ability to get maxed out.
R (Crescendo)- Strikes a Gold chord that makes the enemies hit dance for 1.5 seconds. Of course upgrade this when you can.