This seems like an obvious question and many people have successfully conquered it and set up a standard for reporting. Every once in a while it falls apart and people get blindsided by extra requests that they did not expect but for the most part it works fairly well.
However, even when it is well planned, there is often a substantial difference in what people expect. Some of your stakeholders will want every detail of every test result, defect, and metric that you can generate. They will look and evaluate and ask questions. Others will want to concentrate on the highlights and only investigate when there is an obvious problem that is impacting the project. The last category might be summed up by a comment I heard at one Project Meeting addressed to the test manager and coming from the biggest stakeholder: “As long as you say it is okay; I don’t want to hear anymore”. We removed the actual names to protect the guilty!
While we will come back to this question in a couple of weeks and welcome your input in the interim, one obvious comment comes to mind immediately. Test tools have had a huge impact on this aspect of testing. The ability to record almost everything, drill down, add comments, set statuses, and move items from user to user has facilitated reporting.
In an interesting story from one client a long time ago, the layers of management made the whole process spin out over two weeks from the time the test was actually done to the time the report was consolidated for the last layer of maangement. We have moved a long way from that!