The best lectures, like any good talk, invite students to think imaginatively and conceptually about a significant theme or problem. They do more than "cover the material.” a good lecture always offers a point of view and an entry into a field of study. It is not, however, the ideal platform for a complex scholarly argument or a massive transfer of data. 

The goal is to illuminate a topic, not to baffle students with its nuances or to overload them with information.

You should also try for a relaxed, conversational tone; allow yourself to think out loud, and engage with the material as you present it. It's usually a mistake to rely extensively on a verbatim text, which can result in the kind of mind-numbing performance often parodied in television and movies.  If you can present the message in a narrative form, you are taking advantage of a natural feature of cognitive receptivity.

 So the successful lecturer is, above all else, a good storyteller. If you think back to the most memorable lectures or academic talks you have heard, you will probably agree.