The following is from William Zinsser’s classic On Writing Well.  His comments can just as easily be applied to preaching.

[T]he secret of good writing is to strip every sentence to its cleanest components.  Every word that serves no function, every long word that could be a short word, every adverb that carries the same meaning that’s already in the verb, every passive construction that leaves the reader unsure of who is doing what – these are the thousand and one adulterants that weaken the strength of a sentence.  And they usually occur in proportion to education and rank.

William Zinsser, On Writing Well (Collins, 2006), 6-7.