In addition to it being useful to develop a sharing plan early in your research process (it can help guide some of your data management processes), the International Committee of Medical Journal Editors (ICMJE) released a statement in 2017 saying that anyone hoping to be published in one of their member journals must include a data sharing plan in their ClinicalTrials.gov registration.
ICMJE included a helpful table that details recommendations for what to include in the data sharing plan. Here are the questions you should aim to answer with your data sharing plan:
Open the PDF below to view the table which includes some examples.