Personally, if you have solid professional knowledge and are good at theoretical research, you can write substantive law, such as civil law and criminal law; If the law is applicable, it can be written in the direction of procedural law, civil litigation and criminal litigation; It is easier to write the history of the legal system. After all, the legal history is not too theoretical, as long as you know a little and add your own understanding. Moreover, the information is easy to find, and there are still quite a lot of historical aspects. I have written Sun Yat-sen's "five-power constitution" thought before, which I personally think is easier to write!