There are levels of lucidity.
The initial level that qualifies it as "lucid" denotes the fact that one is aware one is dreaming at some point during the course of the dream. At first, it is often a fleeting awareness. With practice, one can keep hold of that awareness through entire dreams and finally come to a point where one has control over the content and direction of the dream.
....
see:
http://www.lucidity.com/
This book is a pretty good introduction to the subject:
http://www.amazon.com/exec/obidos/IS...460219-0335321