During this phase you plan for which data is needed to answer your research question, and how that data is going to be managed during as well as after the project.
It is wise to write a data management plan (DMP), using either a tool provided by your university or DS wizard provided by SciLifeLab. The main benefits of writing a DMP are to document how the data is managed and identify possible gaps in the current data management practices. Think of the DMP as a checklist to go through when planning for a new project.
High quality science is often only possible if the infrastructure resources you intend to use get involved already in the planning phase of a project. Consultation and advice regarding data management planning, data generation and data analysis are offered by NBIS and SciLifeLab units. Many institutes / universities have established research data offices which provide guidance and support regarding data management questions. There might also be some policies regarding research data, from funders or universities, that you need to be aware of and adhere to.
Also, some resources have specific application periods and thus needs to be contacted well in advance. If your project includes sensitive (human) data, note that there are ethical and legal issues that you have to consider, such as apply for an ethics approval, establish necessary agreements and report the data processing to your Data Protection Officer. See the page on Research involving human data for more information.