The lecturer should give the audience full reason to believe
that all his powers have been exerted for their pleasure and instruction.
Yesterday I recommended a short text by Paul N. Edwards (School of Information University of Michigan) called How to Read a Book (v4.0). Looking on his essays page, there is also an excellent text about How to Give an Academic Talk, v4.0. It is a very good summary of the typical mistakes people make in giving academic talks. Personally, I usually recommend these books by Reynolds to my students and highly encourage them to watch some TEDtalks for brilliant examples of very good orators. I’m going to include this text as well.
BTW, he recommends at one point recording yourself — did you know that many notebooks have a built in camera that can be used for this, or that your cellphone/smartphone will probably also do a decent job in doing so? I remember a time when I took a presentation course at the local adult education center and it was something special to be recorded by a video camera (on tape!) when giving a presentation. Today we have all these tools to improve ourselves — why not use them?
Highly recommended — Edwards, P. N. (2010). How to Give an Academic Talk.