The Adaptive Brain, Volume Set (Advances in Psychology Ser) (v. 1) Book

"You can speculate anything about an isolated dream; but if you compare a series of, say, twenty or a hundred dreams, then you can see interesting things. You see the process that is going on in the unconscious from night to night, and the continuity of the unconscious psyche extending through day and night. Presumably we are dreaming all the time, although we are not aware of it by day  because consciousness is much too clear. But at night, when there is that  abaissement du niveau mental, the dreams can break through and become visible."

I read this one as an introduction to his works which was a series of five lectures he gave at the Institute of Medical Psychology (Tavistock Clinic), London in 1935, and also goes by the name Tavistock Lectures.

With the set of lectures, Jung has tried his best to cover the basic overview of his works starting with the structure of the conscious and the unconscious mind, methods used in the investigation of contents originating in the unconscious psychic processes and methods involved i.e. the word-association method, dream-analysis, the method of active imagination followed by brief notions on archetypes and some mythological references and eventually some specific debriefing of the phenomenon of transference during the course of dream analysis.

Jung's witticisms and clarity of thought can be heavily found in these lecture transcriptions and is something personally hard to digest and take it for an individual in an intellectual basis. This is a good introductory book in parallel with Memories, Dreams, Reflections (1961) for the proper and further exploration of Jungian Psychology.