My wife and I write together. Our latest novel (all most done, just revisions on the last chapter) I plotted and wrote 67K, also I put in plot tags where my wife dropped in her half of the story line. The two of us together create better content than either of us alone.
The real deal though is to run on the popcorn system. That is, keep writing. No one pops corn one kernel at a time, the reality of the publishing world is that, a book can take upwards of 4 years to hit print. Even books written on contract run a year or more from deal to publication. Research your market and write, write and keep writing.
Brandon Sanderson had the seventh novel he had written come out as his first book, just as he had finished his eleventh novel. That netted him a contract, and his ability to stay two years ahead of his deadlines, gained him (in part) the WoT contract.
So Write, Write more, and then keep writing. The trick is to fill the pipeline and get in front of the curve. And (you guessed it) Keep Writing. (Grin)
Best of luck,
Kevin