Over on her blog, Nancy Kress asks whether you should start a story with a dream.  And I see plenty of stories, particularly those meant for younger readers, that do so.  It's an easy way to introduce quick drama (it's not usually a dream about waiting in line at the DMV) and maybe some background information, and then start the story with a "waking up" that is both metaphorical and real.

Two problems.  One is just a matter of building reader trust.  When I read a story starting with a dream, my first thought is that the writer couldn't figure out a better way to start the story.  I started the first draft of my next book After the Victory with my main character having a dream and waking up.  It does start in the middle of the night, with an emergency alert.  But my suspicion of the trope, rather than any inherent lack of sense to it, made me remove it.  Too sensitive to being called a lazy genre writer?  Maybe.

The second problem is that real dreams make no sense whatsoever.  It's like building a narrative based on the names of cars that pass you on the highway.  Any coherence is imposed retrospectively, but a conscious mind that doesn't have any privileged access to the sorting and discarding processes of REM sleep.  A sensible dream that conveys useful information to the dreamer, or even predicts the future, is another piece of...let's say casual workmanship on the part of the writer.  Of course, dreams have served divinatory purposes all through history, so I'm kind of swimming against the current of human expectations in general here.  It is not unreasonable that a character in the story would think that a dream conveyed useful information.  But that's the different between what the characters think, and what the reader is supposed to think.

Dreams can't bear the weight that has been put on them by fiction.  Any writer should be wary when a dream presents itself as a solution to a narrative problem.  And any reader should be wary when they come across one in fiction.  Make sure the writer is giving you good weight.  Your time is valuable.