Check out the May Issue of Deep Magic. Brandon Sanderson‘s got an article on how he takes ideas and turns them into stories.
Here’s a quote from the article that reinforces some of the things I’ve been riffing on lately:
“One idea, no matter how brilliant, does not make a novel! One idea probably won’t even make a short story. I’d say that a novel needs at least six, a short story at least two. The numbers will differ, but the thing to keep in mind is that you can’t generally carry a story on just one concept.”
When a writer lets those ideas grow without writing them down, pretty soon he has a novel with fifty ideas. I don’t know where the cut off point is on how many ideas to put into a book, but I’d say that fifty as way too many–at least in a book by a beginner. Somewhere the ideas multiply until the writer loses control of the book. There’s no longer a focus, and if the author isn’t focused, then the reader will lose interest.
Read Brandon’s article! It’s full of great advice. Plus, he talks about his new novel Mistborn: the Final Empire coming out this July from Tor Books. When the book comes out, look for the person who did the maps and the interior art. I think you’ll recognize his name. 
Oh, and the book is an excellent read; one of the best fantasies I’ve read in years. So don’t buy it just for the maps.
–Stewart!