In a recent study regarding found that there are three major parts to messages we communicate. The study was interested in measuring how effective each element was in the overall impact of the speaker's message. The results were astounding:
How often do we focus on words when it comes to public speaking? Or worse, how often have we tried to write out a speech, memorize it and then perform it? If your answer is more than once then that is once too many. The fact is that this is a rampant and TERRIBLE TECHNIQUE when it comes to public speaking. Quite simply, all it takes is one word to derail the whole train. Instead, the best of us perform the Extemporaneous Style of speaking (slightly guided). At best, writing out and memorizing a speech will leave the impression of a disconnected drab robot. Whereas extemporaneous speaking gives you an outline and allows you to fill in the words based on your experience. This method allows you to focus where it counts- on Body Language or Tonality... the words will follow.
When selecting a topic for public speaking, pick something you are passionate about. Can't find your passion? Ask yourself-What do I do for fun? What do I care about in the world? When speaking with friends, what do I get excited about?
Unless you work in a tire shop, your boss is never going to ask you to give a speech to your colleagues about changing a tire, so why select a topic you know nothing about. In the real world you speak because you have earned the right to do so. Your topic selection should reflect nothing less.