Ezreal vs Xerath

Land Mystic Shot (Q) as often as you can: each hit lowers all your cooldowns and adds a Rising Spell Force (passive) stack.

Detonate Essence Flux (W) with a spell rather than an auto: the orb deals its damage either way, but a spell refunds its mana cost plus a bonus.

Save Arcane Shift (E) to escape unless the kill is certain: it's your only way to reposition, on a 26 to 14 second cooldown.

Cast Trueshot Barrage (R) across the map to finish a fleeing target: it hits everything in its line, but deals less to minions and non-epic monsters.

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.