What does Ray Bradbury assume you already know before reading Fahrenheit 451?

There are many allusions in the novel.  An allusion is a reference to history or literature.  The allusion works if you already know something about the history or literature being mentioned.  For example, there are several references to famous people that most people would know, so that the reader understands what Montag’s society has given up when it banned books. 

When his neighbor Clarisse asks Montag how he feels about banning books, he brings up...

There are many allusions in the novel.  An allusion is a reference to history or literature.  The allusion works if you already know something about the history or literature being mentioned.  For example, there are several references to famous people that most people would know, so that the reader understands what Montag’s society has given up when it banned books. 

When his neighbor Clarisse asks Montag how he feels about banning books, he brings up the firemen’s official slogan.  It mentions several authors that readers will know, using alliteration with the days of the week.

"Do you ever read any of the books you burn?"

He laughed. "That's against the law!"

"Oh. Of course."

"It's fine work. Monday burn Millay, Wednesday Whitman, Friday Faulkner, burn 'em to ashes, then burn the ashes. That's our official slogan." (Part I)

Bradbury does not have to assume that his reader will know all of these authors, but he hopes that his reader will recognize one.  It will connect the readers to Montag’s world, and connect Montag’s society to ours.  It reminds the reader that Montag’s world seems to be based on ours.

Bradbury does this again with the founding of the Firemen. 

"That's rich!" Stoneman and Black drew forth their rulebooks, which also contained brief histories of the Firemen of America, and laid them out where Montag, though long familiar with them, might read:

"Established, 1790, to burn English-influenced books in the Colonies. First Fireman: Benjamin Franklin." (Part I)

The story is obviously false, but readers will connect with this bit of revisionist history, and it will hopefully make them stop and think about what is really happening here.  Saying that one of our beloved historical figures, Benjamin Franklin, founded the firefighters will make the readers stop and think about what is going on.  They will wonder why the firemen would say that.  Connecting Franklin’s name to the firemen gives them legitimacy.  Maybe not everyone in Montag's society is as supportive of the book-banning as it seems.  Of course, we find out later that this is the case.