Interesting content, confident delivery and appropriate language are the three essential elements of any effective speech.
This short (46 slides) presentation explains each and outlines the ideas students need to consider when making their choices.
A useful resource for introducing concepts of spoken English to secondary students. Examples are kept to a minimum so that teachers can use ones that are appropriate to their year level.
This is part of a larger body of material on spoken English but is perfectly able to be used as a stand alone.