When starting your research, you'll need to get the big picture on your topic. One good way to go about this is to consult a reference source like wikipedia. Use this stage as an opportunity to get deeply familiar with your topic: learn the specialized lingo, read about related topics, and identify key themes or issues.
When you search for books, articles, and more, it is a good idea to carefully select keywords to reduce your results to only sources that are relevant to your topic. Because you've already familiarized yourself with the key themes of your topic, you'll probably have a handful of keywords to use.
Use these tips to super-charge your search results:
Try these databases to narrow yourself to good sources of Game Design literature.