If you are asked to teach a subject which you never taught what will you do?

Well you can use the magic power of (preparation) through studying, consulting specilatists and surfing the internet. If you don't absorb the method you're dealing with or don't know much about it I advise you not to try it.

Took the intiative & get prepare my self to deliver an introductary secession to students to become a teacher & a student of that subject as well....

If there's a gun pointed at my head, then I will have to do it; otherwise, I don't see why I have to do it. :)