Well i guess the best thing to remember is to make sure you do what they say. If theey give you the title of the article, use it- if not write your own
If they want an interview, speech anything make sure make it obvious that that is what you are writing...have a intro from the radio guy saying "GOood morning and welcome to the breakfast show on blah blah station" or something, you get the point.
My teacher always says if they ask you to write an interview that doesn't specify who with, don't be like Jane Austen...okay, she's dead and that's that.
If its a speech to HSC students (or anyone) don't 'dumb-down' your language, you shouldn't ever have to do that.
Teachers always maintain that the generic essay with just an intro and conc that fits the specified text type is obvious and not good enough...you need to make the entire piece integrated according to what it is...but that's a little hard and I don't do it all that well often and go okay...
Good luck!
)