For what it's worth, writing good PRs applies in more cases than just AI generated contributions. In my PR descriptions, I usually start by describing how things currently work, then a summary of what needs to change, and why. Then I go on to describe what exactly is changing with the PR. This high level summary serves to educate the reviewer, and acts as a historical record in the git log for the benefit of those who come after you.

From there, I include explicit steps for how to test, including manual testing, and unit test/E2E test commands. If it's something visual, I try to include at least a screenshot, or sometimes even a brief screen capture demonstrating the feature.

Really go out of your way to make the reviewer's life easier. One benefit of doing all of this is that in most cases, the reviewer won't need to reach out to ask simple questions. This also helps to enable more asynchronous workflows, or distributed teams in different time zones.