Today, take a look at your body of writing, published and not-yet published. Like, actually stop and inventory it. From there, create a list of ideas on which to further expand, follow-up, or refresh what you’ve already written in order to create new pieces of writing from them.
This, as a regular practice, is a solid tactic to help shore up your body of work around topics you already write/know about. It helps expand your reach in those areas, and helps you establish your expertise in a given area more deeply.
And, remember, What to Write About: The Big List is always available for you, too, a list filled with all the posts here about generating topic ideas.