For myself, I choose words that resonate with me. They're usually simple, and in my first language-- German. Either a word to describe what I'm trying to do, or just a simple count to three to help me concentrate.

[Or just a snap of his fingers -- but that's higher level stuff that he'll get to once she masters the basics. Because of course he's already thinking that far ahead -- even if he figures the possibility of being outed as a demon and spurned away will come sooner or later.]