What is the key to making extemporaneous speech sound professional and natural

Well mainly extemporaneous speeches can be hard,  finding the right words without advanced notice may not be for every speaker. But trust me! No need to worry :) The extemporaneous speech is a perfect balance This speech involves the speaker's use of notes and some embellishment to deliver a speech. To clear this up, a speaker who uses this method would have note cards or prompts that guide him from point to point, but he uses his own words as he goes along. What makes this different than an impromptu speech is that he has a loose guideline for his speech. He did not memorize anything he just used cues to know where to go next.
There are advantages but there are disadvantages to this type of speech sadly :(  For one, the audience will think you are a genius. You used few notes and appeared to know everything about the topic. But this is not something that can be done quickly. The same fact finding and research used for other types of speeches must be used here. The speaker also must rehearse this speech for timing, rhythm and flow. Now, if shooting from the hip is not your style, you may want to consider reading your speech :) But ya. I hope this is better. XD sorry about that.