I'm still working my way through all the Bond books, and I'm very near the end now, thankfully. You Only Live Twice is the penultimate book written by Ian Fleming in the Bond series and, many believe, the last he completed by himself. It's certainly the last published in his lifetime.
Although it bears some similarity to the film, the story is very much different. Bond is recovering following the death of his wife (of one day), Tracy, at the end of On Her Majesty's Secret Service, and has become a rather second-rate agent because of his reaction to Tracy's death. M, as one final attempt to get him back on track, sends Bond to Japan, where he meets Tiger Tanaka who gives him an intriguing task, before teaching him the ways of the Japanese.
Inevitably, since this is a Fleming novel his characterisation of the Japanese ranges from the patronising to the outright racist. Clearly Fleming is writing in the 1960s when attitudes were different, but to a modern audience, his pronouncements on the Japanese are rather jarring.
Much worse than this for the reader, though is that by this period in his Bond writing, Fleming had fallen into a rather tedious groove. Bond goes somewhere in the world, meets another agent who tells him about a terrible person who lives in a strange location and is plotting something awful, Bond, one way or another gets rid of them, meeting a young woman along the way that he ends up having sex with.
You Only Live Twice fits entirely within every aspect of this outline, and therefore, alongside the lazy racism and one dimensional characters, if you've read almost any other Bond book, chances are you'll find it difficult to distinguish the plot from any one you've read before.
Bond books are, by their nature, rather predictable, and I wouldn't recommend doing what I'm doing and reading all of them. If, for some reason you are interested in reading a Bond book, though, I also wouldn't recommend this as a good place to start*.
* If you are interested in starting with Bond, I'd recommend reading the short stories. They're pleasingly short, more varied than the novels, and give you an good insight in how well you'll be likely to cope with Fleming's racism and sexism.