The great thing about GEB is that Hofstadter basically assumes no prior knowledge from the beginning of the book - he just asks that you pay close attention and exercise your analytical mind. You'll then soon start to notice the patterns, jokes and puzzles in the writing, and how they all relate very closely to the ideas presented in the book.
Note: the book isn't necessarily out to prove anything, and if you're looking for a massive 'aha!' moment towards the end of the book, you'll probably be disappointed. It's just an incredible journey down the recursive rabbit-hole that ties together mathematics, formal logic, linguistics, biology, computer science and loads more all through the extremely deliberate use of language throughout.
It still blows my mind, but requires a good amount of concentration, re-reading and note-taking - which seems fair enough as I can't even imagine how long it took Hofstadter to write!