So I'm just starting out at a high school in Pohang, I've been told by the person I'm replacing not to do an introductory ppt, but everyone here seems to think it's a good idea?!
Also, setting down the rules and such, do you think it's better to set them down the first day? Fifty minutes seems a lot of time to fill with introductions! Discipline seems to be kind of important, especially here  :S

Hi
Don't worry about your first class too much!

Just make an introductions about yourself, home town, hobbies, and interests. Then find some games.
I'm doing human Bingo and 2 truths 1 lie activities.

If there's extra time get the students to think of questions to ask you :)

Also smellyhelly welcome to Pohang, I'm a high school teacher in Pohang as well! :D

my co teacher also said introducing yourself is a good idea, and usually what the native teachers do for the first class. She said to allow time for the students to ask you questions as well. I am still very much nervous about it, especially seeing how my co teacher is new to the school.

I'm pretty worried about my own intro being understood. I try to talk fairly level and clearly, but I think they'll just be staring at me blankly the whole time.

Best just to talk normally and make appropriate PPT aids for them to understand. If nothing else, smile and make jokes.

I'm guessing you may have had your first class by now but an intro lesson is crucial! Whoever the teacher is telling you it's not is setting you up for a fall.  It's your chance to make an impression.  As long as it's interesting, includes some details about where you are from, some cool things you've done, all the awesome places you've been to etc etc....it'll make a great impression.  My intro involves about 20 minutes of me asking them to guess true of false about my age, nationality, siblings and so on and then me turning it on them and doing as another person suggested, 2 true one false with the students.  It gives you a chance to walk around and learn a little about them.  I normally put on a video of me doing something cool like skydiving or whatever you might have.  Making a good impression is good for getting them to find you interesting and motivating.  Going straight to a lesson would be so weird.  I have no idea why someone would tell you to do that. 

Best of luck, you'll be fine.  Just dazzle them with your newness, it's not hard!

@Rowdie That's basically how my classes went as well.

@ kim2240 - mine went well in the end, my intro was really short too but i got them playing two truths and a lie afterward and if you explain it really clearly (with examples) they get into it. takes up the rest of the lesson too :)