Like most books of this type it is patchy with some of the entries as entertaining as the books the writers produce and one or two being so utterly bereft of soul that you lose the will to live before you're past the first page, leaving me to wonder why the writer bothered to put pen to paper in the first place. Also, there's far too much emphasis throughout on horror rather than fantasy or sci-fi but my feeling is that that was a decision based on trends of the time more than anything else. What they do all have in common though is that they are slim, each chapter being barely a few pages and each is big on an idea and very light on specifics which makes the generalised nature of the advice not as useful as it might be.
It's not a new book, I bought mine second-hand from Amazon and it was published in the 80's but the basic principles of telling a good story and then selling it are pretty much the same as they've always been - in this case mostly common sense rather than any great insight - but it does mean that the lists of helpful publications at the back are almost completely redundant and of course there's no mention of the wonderful world of the internet and it's part in the selling and promotion of your tomb.
So while it does contain one or two useful gems it's not a book I'd recommend by any manner or means and if you really want something like this I'd stick to Orson Scott Card's 'How to Write Science Fiction and Fantasy' or David Gerrold's Worlds of Wonder, both of which are infinitely better books.
How to Write Tales of Horror, Fantasy and Science Fiction is published by Writers Digest Books and is available from Amazon, Blackwell and all good book stores.