FAIR guiding principles for data resources, CC By-SA 4.0 Sangya Pundir
Once your project is finished (or even earlier), it is generally a good idea to consider opening your data. But opening your data means doing more than just putting it online. To be considered open, research data must respect the F.A.I.R. principles set by the FORCE11 working group. Your data must be findable, accessible, interoperable and reusable.
To know more about the FAIR principles, check out this document by SNSF, which breaks down what they imply. As you will see, documenting your data and using metadata will make it understandable. Using durable and open file formats will make its preservation and re-use easier. Clarifying usage rights is also necessary, and so is choosing the right platform to host your data.