Don't talk about it, just write it. Blast it out, don't edit it, just get the whole thing down onto 'paper'. Then start editing. Editing for me usually means adding more words rather than removing them. Other authors find themselves removing words.
Also, once you've got the first draft done, you've written a book. Not many people can say that, but many people will say that they 'want to write a book'. They never will.