The majority of knowledgeable writers will tell you not to waste your time and to move on to a totally different project while you wait on responses to your queries and/or submissions.
I'm going to tell you the opposite: write what you need and want to write.
When it comes to writing, I am very serious about it. I have been since I was 8-years-old. Having a fantasy book published has been my dream for almost 3 decades. However life in general went more in the 9-to-5 direction, so my writing was done at odd moments, such as 15-minute breaks at work.
Then I got to a time and a place in my life where I could devote more time to my writing. I became a stay-at-home mom. The first work on which I seriously focused was non-fiction (not just writing, but acquiring and editing). In the past 10 years, I have seen several of my articles and reviews published in Pagan magazines. I also was able to find the time to put into fiction and finally saw 2 of my books released last year.
Currently, I am in the process of querying a novel codenamed "Project Muffin Man". It is meant to be the first in a series, though can easily stand on its own (and I would have no problem altering the ending to ensure that). However, because I do hope to see a 3 to 5 book series with it, of course I have already thought ahead to the books that might follow.
Last year I completed its sequel, codenamed "Project Lemon Cake". Was it a waste of my time to write it, even though "Muffin Man" is neither represented nor under contract with a publisher (yet)?
Not in my opinion, and here is why: I think that when you are immersed in a world and its characters, you should go with the flow of inspiration. Fighting against this is what leads to the dreaded writer's block, or writing that is so forced it doesn't quite "fit" or flow well (versus those other times when you were writing for the joy of it).
In addition to that, I had very practical personal reasons for ensuring that the second book was completed and ready to go, should I be so fortunate as to receive an offer of representation or publication.
Despite what most writers will say, there is no rule whatsoever that says you cannot write your sequel, or the next book in a series. If you are "feeling it", then write it.
Simple as that.
Copyright (c) 2011 Wendy L. Callahan