The first element in the preparation of a lecture is research. How much research you undertake for each lecture will, of course, depend on how much study you have already done on the subject. Gather enough information so that you can be selective. If your lecture includes everything you know about the subject, it may be dull because you have not sorted out what is essential and interesting from what is subordinate or dispensable. At the same time, do not spend so much time gathering material that you do not have time to organize and polish the lecture.
Organization is the second element of lecture preparation.
Some kind of organization is necessary not merely as a guide when you give the lecture, but also so that students can quickly grasp the overall concerns of the lecture. It may be helpful to write a brief outline on the board at the start of a lecture so that students focus on your overall organization. Since the students lack the background in the subject matter that you have, you will need to organize the lecture to make explicit relationships and connections that you may take for granted. Topics or controversial issues may be used to organize a lecture. View each lecture as a kind of unity that has a carefully planned beginning, middle, and end.