Reproducible research depends on having good systems for organizing and documenting your research. These resources provide recommendations for setting up and maintaining well-organized projects.
There are a lot of things to document as part of your research! If there is a metadata standard for your discipline that is a great place to start as it will tell you what to document and how. If you know what repository you will be using for your data check and see if they recommend a data or metadata standard. Read more about metadata standards and see if there is one relevant to you below.