I'm sure you've heard the phrase, "Good things come to those who wait." It's usually said by parents trying to get a little more time to finish whatever it is they're doing before the kids drive them insane with demands.
In the writing world, this was something I was often told, maybe not in those words, exactly, but something to the same effect. "You gotta wait for the agent/editor/publisher to get to your stuff before you can publish." Very true, particularly if you're waiting for one of the Big New York publishers to get back to you.
However, that doesn't mean you have to stop what you're doing or even stop honing your craft. Yes, you've finished your manuscript; yes, you've submitted it to one or several publishers; yes, they've given you a 16 week response time, but you don't have to stop writing. You don't have to wait by the phone/computer/iphone with baited breath.
Now is a good time to write the next book/novella/series of short stories. Don't wait on the editors. They're busy looking at your manuscript. Now is the time to practice some more. WRITE WRITE WRITE. This is the time to get the new story out there because if they turn down your first story, maybe they'll pick up the next one because it's just a little better, just a little more refined, just as little better planned and sketched out.
In each story I write, I improve my story-writing abilities. I've always been good at "telling" the story to folks, but writing takes a little more discipline and refinement. Talking it out, a story is full of colloquialisms and the words "that", "which", and "because"; telling words. In writing, it's a clunky way of reading and it pulls the reader out of the story. Refining the writing to leave out those words but still get across what I want to; wow, that takes practice!
So be proactive in your writing efforts. Submit to the publishers, query the agents, and then get back to work on the next story, because as Christina Dodd once put up on Facebook: "Professional writers are only amateurs who never gave up." Truer words were never written. :)