Self-plagiarism and citation when working on 2 papers simultaneously Say you're working on two papers A and B simultaneously, and the content and topic of the papers partially overlap such that normally you would be required to cite paper A in paper B. But since both papers are being written simultaneously how do prevent self-plagiarism? 

Should you cite paper B in paper A and vice versa, even though neither is published yet?
Yes, I would cite paper A in paper B, and I would cite paper B in paper A. Initially the citation would be something like “in submission” with a URL for the referees. As both papers work through the pipeline, that citation would evolve into either a refereed publication venue if possible, or a preprint server if not, to ensure that future readers can follow the link.

On the other hand, I would also write both papers from scratch, without sharing text between them, because (in my experience) that leads to better-written papers. So self-plagiarism isn’t an issue.