Maybe an obvious one, but at my last org I often wished for more emphasis on keeping patch sets SMALL. I might have liked some kind of soft ban against putting huge patch sets up for review. I'm talking like 1000+ line stuff. In my experience, no one wants to review those; it's incredibly tedious.

I say "soft" ban because there are exceptions. I don't mind huge patch sets if the changes are proportionately trivial: One example is mechanical search-and-replace jobs on large codebases. But the 3000-line new module that just gets dumped on reviewers all at once is in bad taste. It's the responsibility of the author of the code to ensure that it is broken up in a way that makes reviewers' job tolerable. My opinion.