The first step in researching employers is to get to know the firms or organizations and their practice areas and industries. This will tell you if the employers' interests coincide with your own interests.
Once you confirm your interest, conduct a more thorough search of the employers by reading news articles about them, their recent cases, their attorney biographies, and interesting or controversial topics in their practice areas and industries.
If you are researching a specific employer, begin your research on the employer's website. Though it is a promotional site for the employer, it will provide you with good foundational knowledge on the employer's location, key practice areas, and prominent attorneys.
Other databases allow you to search for employers by type (firm, government, public interest, etc), practice areas, locations, diversity, among others: