Determine the Content
Once you have your purpose sorted out and you know who your audience will be, the next step is to decide how much and what type of content you need. Discuss these points with the person who gave you the assignment.
Then decide how much information you need to provide balance for the opinions, judgment, or advice in your report. For example, if your purpose is to investigate a problem, you'll need to give background information about the problem, then provide details of different solutions that have been attempted and evidence of the results.
If your purpose includes instructions to provide suggestions for alternative solutions, you'll also need to give your recommendations (based on the information in the body of the report).
In one of our examples above, the purpose was, "to investigate the link between kelp beds, pollution levels, and loss of fish stocks in X." One way to approach this would be to investigate the different types of pollution in the target area, then examine the impact this has had on the kelp beds. You could then provide information from industry experts about changes in fish numbers and species in the area before making your recommendations about the best way to combat the loss of fish stocks.
If your report was written for a general audience, it could contain more interviews with fishermen and local residents who provide evidence about what conditions used to be like. Then owners of various factories and businesses that may have contributed to the pollution levels could give their side of the case.