In general, using reference materials is the best way to begin the research process. You may have already completed this step while preparing to write your proposal, so this may be the least useful tab. However, if you find yourself getting stuck, or unsure of where to go, reference sources may be a good place to start. In addition, you can sometimes follow the research trail of a reference source to find additional, relevant secondary and primary sources.
Below are a few reference databases that may be helpful as a starting point for your reasarch:
