Research is a recursive process. You may find during your research or writing that a particular area needs more research and that is okay.
Organizing your research will make the process easier. Make sure to use a research log to track your searching.
Feel comfortable asking for help. Faculty members and reference librarians are useful resources.
What types of sources will you need? Well that depends on what you are writing about. Scholarly legal articles often include other scholarly articles, treatises, news, and primary sources such as cases, statutes, and regulations.
Before doing any additional searching, read your preemption materials. The materials that you have gathered in your preemption searching should have provided you with many materials including some that set out the background or history of your topic. Your gathered materials may also provide citations to other resources you will want to read.
Once you have read your preemption materials, you have a number of methods for expanding your research.