Sona vs Xerath

Choose the spell you cast before Power Chord (passive): after Hymn of Valor (Q), the auto deals more damage, and after Aria of Perseverance (W), it weakens the target.

After each spell, move close to your allies: your aura gives them a damage, shield or speed bonus depending on the spell.

Hit champions with Hymn of Valor (Q) and shield allies with Aria of Perseverance (W): Power Chord (passive) gives you ability haste, then reduces the cooldown of Crescendo (R).

Save Crescendo (R) for when several enemies are in front of you: it stuns them all and deals damage to them.

Keep minions between you and Xerath: Shocking Orb (E) stuns the first enemy hit, for longer the farther it has traveled.

Don't stand still, and change direction often: Arcanopulse (Q) hits a target moving forward or backward in a straight line much more easily.

If you can engage, go in while he charges Arcanopulse (Q): he slows down by up to 50%, and he has no dash to escape.

If you have CC and can reach him during Rite of the Arcane (R), use it: he channels the ult, and interrupting it stops his shots.