When working on a research project, its is important to have access to large and diverse data sets. Open data is data that can be freely used and redistributed by anyone. Open data is subject at most to the requirement of attribution.
Some general qualifications to working with open data:
Use your best judgment when working with open data. As open data can be redistributed, make sure you are getting data from its source to ensure data fidelity.
Open data can be found anywhere. The first step is to refine what your are looking for. This could include subject matter, type of data, time period, particular demographics, etc. It is important to start broad and continually narrow down your search to find data that is appropriate for your research.