If you decide to submit your data to a repository, it is a good idea to license your data. Licensing data allows researchers to clearly state how they want their data to be used, and makes it easier for others to reuse the data. While data themselves do not fall under copyright protection, datasets and databases do, and the easiest way to protect your copyright while allowing access is by attaching a license.
Before deciding what license to use, you must first ensure that you yourself have permission to license the data, for only the rights holder can grant a license. Once you are sure you can grant a license, you must choose which license to apply. Make sure to check with your organization or repository as they might recommend a certain license or provide one for you.
The most common data licenses are from Creative Commons and Open Data Commons. Both of these organizations have standard sets of licenses that allow data to be used in different ways.
Alternatively, you can apply a waiver to place your data in the public domain and allow free and unrestricted access. The Creative Commons Zero license (CC0) is the most popular copyright waiver.