I just started doing classes myself. Would of course want to say my sifu insisted but truth be told I was the one approaching him on the subject, knowing he wanted someone to take the role.
For me it felt tough prior to first class, reading all material I could find and planning over and over again what to do during class.
My first class came and it became a complete mess. All those drills I do myself and others which we have done in class, it turns out could not be done due to new students or a room that was smaller than it seemed when I train in it myself.
Second attempt I redid the whole thing and people went away tired, sweaty and smiling. Now I still struggle to come up with good drills, not just because they are good but because they might lead the students to a point where I myself want to train and evolve. So my quest is getting them to that level as soon as possible.
It is a work in progress but if there is one thing I learned. Do what you yourself want to do, allow failure and learn from it. And all feedback is good feedback, even the critical one.
You might have more advice as I am new to teaching, not a thing that comes natural to me being a tutor. My wife laughs at the idea of me being a teacher, something about me not having the patience to deal with people that can not grasp what I am saying.