If you're creating a data management plan as part of a grant, the specifics of the plan will depend on what your funding agency asks for. Some basics to think about that most agencies will ask for include:
What types of data will you collect?
In what format will your data be stored? What file types will you be collecting?
How will ensure sensitive data is secure?
How will you make it understandable to future users? Will a specific software be needed to open the data files? What notes about your data will be made available?
What policies and procedures will you have to allow sharing and re-use of your data by others? Will your data have a Creative Commons license?
How will your data be archived and protected, and for how long?
How and where will you share your data?
The FAIR principles describe how research outputs should be organized so they can be more easily accessed, understood, exchanged and reused. FAIR data, data that's findable, accessible, interoperable, and reusable, is data that follows certain guidelines. This guide has details about those guidelines in more detail.
Borghi J, Abrams S, Lowenberg D, Simms S, Chodacki J (2018) Support Your Data: A Research Data Management Guide for Researchers. Research Ideas and Outcomes 4: e26439. https://doi.org/10.3897/rio.4.e26439