Ongoing, but a common advice is to get started in an onboarding phase
Mastering academic writing enables you to efficiently communicate your research and position yourself in your academic field. Writing is essential for a researcher. As a PhD candidate you will produce a dissertation (research articles or a monograph) as well as conference papers and more.
Here are some topics within the academic writing process you may find useful to brush up:
Referencing
Word choice
Developing good writing habits