Yes, I'm currently writing a novel.
About half is written (and partly polished), the rest is in note form with the plot sorted out and some of the more pivotal later scenes roughly sketched out. I say roughly, because while those scenes have got material in them that's crucial to the plot, it's no point finishing them off, because I need to allow for character development and those odd moments of insight that bring depth to a piece of work.
Discipline is required, yes. But writing is also enjoyable. Not just the actual putting down onto paper, but playing around with ideas, observing life around you, creating characters and places and stories out of your imagination and experiences.
I've actually taken a bit of a break from the novel recently, but that's been to do the research for, and then to write an 11,000 word dissertation tracing the history and provenance of a particular racing car. Which, incidentally, I put the finishing touches to last night. I'm not going to be popular, as I've managed to turn what people thought they knew about the car on its head.
Anyways, if you're looking for one of those "How To" books, then I'd suggest looking for a copy of Michael Legat's "Writing for Pleasure and Profit." It's an oldie but a goodie, and is packed with some sage advice.