Minecraft wiki entry for Combat, associated text: Step 1: Equip the elytra and armor for the remaining armor slots.
Step 2: Jump and use fireworks to speed up the elytra. Fly to a place where the player can safely fire at the target.
Step 3: Fire repeatedly, until target is defeated or until the target gets too close.
Step 4: If the target gets too close, repeat step 2 and 3.