A data management plan (DMP) is a written document that describes the data you expect to acquire or generate during the course of a research project, how you will manage, describe, analyze, and store those data, and what mechanisms you will use at the end of your project to share and preserve your data (Source: Stanford University Libraries)
A DMP is required as part of your grant proposal by many funders, BUT planning for good data management, data sharing, and data preservation should be a part of your project plan and integrated throughout the workflow. Plan for this at the same time you write your DMP. To learn more about best practices for good research and data organization and writing DMPs:
While the basic format of a Data Management Plan will be similar from funder to funder, each funder may have specific sections of information that they require.
The DMPTool has templates and requirements for many funders available on their site. As they state, "Templates for data management plans are based on the specific requirements listed in funder policy documents. The DMPTool maintains these templates, however, researchers should always consult the program officers and policy documents directly for authoritative guidance. Sample plans are provided by a funder or another trusted party."