I have been creating a project report for Google Summer of Code 2021 and have got some very helpful suggestions from my mentor Federico. We believe that it will aid my other fellow GSoC students and therefore I am sharing them with you, through this mail.
1. Give priority to important ones
Try to highlight your most interesting work at the top by creating them as a topic instead of writing them as sub-topics. Explain each point and mention why you did this, what kind of features are being offered, what kind of change you have made, and explain the reasons. Those which are less important keep them at the end. You do not need to write much about them.
2. Add screenshots
Add screenshots of your work in each topic if possible. It will help the reader to understand the work or change.
3. Never miss documentation
If there is any chance to provide links of docs then, please provide for users who can find more details of your work.
4. Do not use URL
Instead of showing URL as anchor text, use words (eg: heading of the linked docs or titles of the pull requests).
5. Focus more on results:
Instead of focusing on the development process try to add details about results and changes and always keep in mind that you are not writing this for only GSoC. You have to extract the best outcomes from your experience and the project which would become helpful for the users reading it even after 5 years.