Even though he was already aware of the fact that she didn't know how to properly use a weapon of any kind, it always shocked him--in the sense that whoever had taught her waterbending had not shown her how to use a weapon of some kind alongside it. Both he and Azula had been taught swordsmanship while they learned firebending, though Azula chose to purse more difficult bending and some acrobatics while he kept up with his swords. He knew that Katara's brother knew how to use that odd boomerang thing and wondered why he didn't take the time to show his sister.
There was more to the art of war the bending; the abilities could only get one so far. Sometimes, you had to use the brute force of a weapon. It was one of the most ancient forms of fighting and was used long before the people of their world learned bending from the dragons, badger-moles, and other such creatures.
"Holding it correctly would be a good start," he teased with a slight smile tugging at the corners of his lips. Had this been a year ago, his words would've been a direct insult to her supposed inferiority. But, they were past that now. He saw her as his equal, even if his Fire Nation pride refused to let him admit that to her.
Zuko moved to stand next to her, holding the sharp blade delicately between his fingers as he plucked it from her grasp and used his free hand to position hers correctly on the hilt. Letting go of the weapon, he wrapped both his hands around hers for the sheer sake of doing so.
"You need to hold it firmly, yet not so tight that you'll strain yourself. As someone who's already a master in the waterbending arts, you already understand the concept of fluidity. You need to be fluid with your movements." He let go and moved behind her, placing his hands upon her wrists and guiding her to swing the blade down and to the left. "Let the blade flow as if it is an extension of yourself, another limb."