These websites provide tips and insight on improving this traditional way of teaching.

Tips for improving a lecture.
Marilyn Lockhart of Montana State Univ. provides 10 tips for improving a lecture.

Suggestions for teaching with excellence.
This compendium of suggestions for good teaching spans multiple sections, including a section on giving good lectures

A series of postings on the Univ. of Chicago Center for Teaching and Learning website about lecturing.
Teaching by the Lecture Method
Lecturing: Using a Much Maligned Method of Teaching
Teaching by Lecture
The Nine and a Half Commandments of Good Teaching

Lecturing with Style.
A website at the University of Tennessee, Chattanooga that provides tips for improving one’s lectures.