How about one per month?
I learn volumes about the art of picture book writing every time I sit down to write a new picture book. But in case you need further convincing, here's my plug for writing 12 picture books this year.
12 Reasons to Keep 12 Picture Books Percolating
1. A portfolio of many projects keeps one project from becoming too precious. And it's hard to remain objective when one project receives all your time and attention.
2. You never know which muse will sing to you. Today it might be picture book #5. Tomorrow it might be #8.
3. You banish writers' block by hopping from project to project.
4. Projects stay fresh as you take time between them and, hence, between reads.
5. One project might inform another. You might cannibalize picture book #9 to make #10 better.
6. When a project is rejected, other potentially winning projects-in-progress help soothe the pain.
7. You always have a manuscript ready for your critique group.
8. You get ALL your ideas out there. Like in a brainstorm, sometimes it's the 5th, 10th, or 12th idea that hits the mark. You might just have to work through the good, the bad and the ugly to get to the GREAT.
9. You never know which project will resonate with a given agent or editor - it's often not what you think. And editors are often looking for projects to match various illustrators – you don't want to be one-dimensional.
10. Getting agent representation for picture book authors is tough, but you increase your chances if you have several projects to offer.
11. Trends come and go. You'll always want to look beyond what's currently "hot." Multiple projects improve the odds that you're looking toward fresh ideas.
12. You'll have 11 more options when an editor asks, "What else you got?"
So don't wait for January. Let the writing begin!
Reprinted from my post in the 12X12 Challenge.