There’s a thing that Denny O’Neil called the Levitz Paradigm (though Levitz doesn’t claim credit for it, pointing out that Stan Lee and Roy Thomas were doing it before him, even if they didn’t formalise it), which is a way of addressing multiple plot threads in an on-going comic.
Simply put, you call one thread the “A” plot, and devote maximum time to it, while also looking in on the B", “C”, and maybe “D” and “E” plots. When the “A” plot finishes, you promote all of the others, add a new “E” plot, and keep going. Hold on, O’Neil explains it better than me:
Basically, the procedure is this: The writer has two, three, or even four plots going at once. The main plot — call it Plot A — occupies most of the pages and the characters’ energies. The secondary plot — Plot B — functions as a subplot. Plot C and Plot D, if any, are given minimum space and attention — a few panels. As Plot A concludes, Plot B is “promoted”; it becomes Plot A, and Plot C becomes Plot B, and so forth. Thus, there is a constant upward plot progression; each plot develops in interest and complexity as the year’s issues appear.
Here’s an actual “Levitz Grid” for the process, which I think is pretty cool:
Not impressed? Try Alan Moore’s Levitz Grid for Big Numbers: