There are a great many factors that will determine the language that you use in your speech. Factors such as - the type of listeners, the ideas you are seeking to convey, the type of speech (informative or persuasive), your own natural style. There is not one perfect set of language that will cover every circumstance.
There are very few rules that cover every occasion;-
Dont’ speak up to your audience
Your audience will quickly sense this and you will lose any goodwill that you had before you started to speak. The audience will think “Who does he think he is?
Don’t speak down to your listeners
Also they will quickly catch on to any inferiority behavior and interpret it as a phoney air. Your speech will be dead in the water.