The first thing is to find the data that you are interested in.
- Consider the following article "The 50 Best Public Datasets for Machine Learning".
- The most well know source of public datasets, Kaggle
- From google https://datasetsearch.research.google.com
- Open data from Lisbon
- Portdata - Contemporary Portugal Database
The second task is to search for Data Vis solutions built on the top of the data you consider and try to find what questions do you want to address with the selected data.
The third task should be to propose your how innovative Interactive Data Visualiution to address your selected questions