A good good public speaker is able to use language effectively to convey their message. Language should be appropriate to the audience (i.e. do not use technical language to a non-technical audience) and engaging so that they are drawn into the subject. Rather than using passive vocabulary, more descriptive words should be used to add a different dimension.
Language can also be used to build word pictures, being precise with descriptions (crimson, scarlet, ruby rather than red) as well as the use of adverbs and adjectives rather than the simplistic. Your evaluator, using these guidelines, will want to see you demonstrate your skills and understanding of techniques such as alliteration, repitition and similies.