Extempore speech is given to selected unknown audience and topic. With this test you will be observed on your communication skills and expression of thoughts on assigned topic. Your confidence level will be on anvil.
Maintaining eye contact with audience in your extempore speech will positively give you confidence and you will benefit two ways. First you can observe face reactions of listeners and second you will create another opportunity to maneuver your speech. While doing this, it is expression of great confidence.
Practicing on variety of extempore topics will gain you different understanding of psychology of audience and you can be successful.
You need to be conscious of the fact that you are being observed for your each word and gestures while you deliver speech as selection panel will objectively judge you on given parameters which they might explain you beforehand.