For your Data Management Plan you need to identify first if there is pre-existing data to help answer the research question, that would save duplication of effort and resource.
If collecting/creating data you should consider the ethical and legal obligations upon your research and how these will impact how you collect, process, maintain, store the data as well as activities at the end of the life-cycle such as sharing, retention for 10 years post project and any destruction required.
Where relevant, consider what any funder may require you to do in relation to data as well as what costs they are willing to cover and any requirements for sharing or preservation.
Contractual obligations may also impact on what can/cannot be done with the data, in which case these should be defined in the DMP.
Costs associated with data creation, processing, storage, back-up, sharing/preservation and other specialist facilities should be costed up as early as possible and described in the plan. You should also clarify who will own the data and persons with various responsibilities for data e.g. Data Management Officer, GDPR roles etc.
Further information on each of these issues and institutional services can be found via the page links below.