Hiya.
With 英会話 schools, you want to provide a very student-based environment with very little teacher talk time. The goal is to get the students to speak and interact a lot. So lecturing, demonstrations, anything involving the teacher speaking more than the students is frowned upon.
I suggest something like this, which is very similar to your suggestion. I'll break it down a bit more.
First, introduce a goal of some sort. "Today we're going to buy a hamburger at McDonald's", or "Today we're going to learn to introduce ourselves". Something focused and goal-oriented, a concept the schools are big on right now because their advertising pitch rests on providing students with immediately effective language useful for traveling and so on.
From there, introduce the necessary vocabulary/phrasing. Anything the students might not know (in this imaginary situation) such as "fries", "napkin", "would you like...with that", etc. It's all based on real world experience and isn't meant to look book-ish or high-brow. It's meant to be immediately functional.
Moreover you want to try to elicit the language from the students rather than, again, teaching/lecturing it. So, e.g. you can say "What do you eat at Mc Donalds?", (a topic everyone can join in on), and that gets them talking immediately and saying stuff. Write it down and use it later, you know, if one student says 'Milkshake' have them order a milkshake later instead of the burger. Ask them what they put on the burger, get someone to say the word 'pickle' so they can say stuff like 'No pickles please' etc.
So, after you set the topic, elicit/present the vocab in an interactive fashion, you finally get them to act it out. All in all, your talk time should be minimal and the 'students' (the other ppl in the interview) should be doing all the talking with minimal guidance from the 'teacher'. Do that that with a harmless metrosexual smile and you're guaranteed a job at an 英会話.
I did a phone interview so.. my smile wasn't an issue thank god.
As for what they want in a person, they want someone who knows as little about Japan as possible but is really REALLY interested in coming here for whatever reason. They want someone who's easy on the eyes and ears and fairly easy-going. Dress professional, wearing a suit is big points, you know, same as any interview.
In the personal interview they will get you to do the lesson thing again. It's important to maintain a very upbeat and smiley lesson. No matter how 'akward' the interviewer pretends to make it, or how confused you are as to what to do next, maintaining that smile and just rolling with the punches in a non-abrasive way is what they want. Just smile.. nod.. that's almost pretty much it to be honest.
You also want to simplify language. So, if the interviewer is pretending to be Japanese and makes an intentional mistake or acts confused, and you have to correct them, don't get preachy and verbose, you want to say things easily and mimic. Instead of "yes well tasty is when something tastes really good and we like it, it's similar to delicious" just go "This sandwich is tasty, mmm" and rub your stomach. That kinda stuff, they love, (as long as it's not overdone or condescending/child-like. It still has to be real-world English not baby-talk).
One thing I noticed, you don't want to be the guy who immediately asks lots of questions about the lifestyle in Japan to the degree that it becomes obvious this will be a big change for you. You wanna be all like "What? In some places they have squatting toilets in the ground instead of proper sitting-ones? Well I'm keen to give it a try!", etc. So basically only ask intelligent/fun questions and only after you're sure it hasn't been/won't be answered.
And that's about all I can remember.
Working at an 英会話 is a joke so one last piece of advice, come here with a goal in mind. Save up cash, learn Japanese, do martial arts, pick up a hobby, whatever your fancy. That way you'll know when it's time to leave and the repetitive nature of the work won't get to you.
Good luck.
