Be polite and assume the other parties are acting in good faith.
The PR shall follow all the guidelines set forth in the repos' PR templates. For the example of electron/electron, this template.
If the PR fixes an issue, the PR must mention that issue in the PR body, e.g. Fixes #123.
Pull Requests whose changes affect end-users should stay open for at least 24 hours. This is to allow for input from all timezones.
Unless other agreements have been made, people should allow 24 hours before pinging folks for review or re-review.
If a PR has a time constraint, the person requesting review should use their best judgement for when to ping people.
A reviewer's role is to work with the PR author to land wanted PRs that are testable and maintainable.
Requesting changes in the service of these goals is strongly encouraged, but always remember the "work with the PR author" clause: we want to land excellent code, and we want its authors to feel welcomed in the community. Ask yourself if other reviewers would agree with your change request.
All PRs should be squash-and-merged with the exception of Chromium upgrades that should be merged in order to maintain commit history.