For the 30-second "demo," remember two things: 1) It really doesn't matter what you're teaching in these 30 seconds, they just wanna see how you engage a classroom. 2) All they're gonna learn from this is how prepared you can be and how well you can do in front of a room. Seriously, that's it. Don't worry about whether your thing is advanced or basic or anything. Don't try to be thorough. Your biggest enemy is the clock, and your biggest asset is the ample prep time you have. The interviewer told me I stood out in my group because I had a whiteboard with all the necessary information pre-written on it. I taught a math problem, and made handouts (Actually just flashcards) with all the steps and numbers on it, the class just had to follow along and fill in the blanks. Remember that the interviewers are going to try and offer the wrong answer to a question, and they're gonna try and ask irrelevant stuff. This is to see how you give feedback or constructive criticism. In a grammar lesson, just explain that these are the grammar rules, in a math lesson, just tell them the right number and we'll check their work together after this lesson. The key is not to get distracted. Your biggest enemy is gonna be the clock in this lesson, so you can't let yourself get off topic. The most common mistakes I saw were pacing - people would end too soon or too late, and it felt awkward. Just make sure you practice at least a few times beforehand, and you'll be fine.