Remember those PubMed Tips & Tricks? Most are applicable to many other online databases. For a comprehensive list of dozens of databases, see the guide to Databases in Public Health.
Grey Literature generally refers to publications -- from government entities, research institutions, or NGOs/IGOs -- not produced by commercial publishers: including reports, market research, theses, conference proceedings, and other documents.
The Public Health Library's Public Health Subject Guides web guide consists of web pages by topic. Each page consists of annotated lists of organizations, agencies, databases, and publications. Topics include:
• International Health
• Maternal and Child Health
and many more.
Google (or other search engines) may be useful for finding grey literature. Improve your search using:
• Quotes for phrase searching:
• Site: to specify a particular site or domain:
"social marketing" site:.org (for a domain search); "social marketing" site:cdcnpin.org (for a specific site search)
• Boolean search statements (eg, OR):
("social marketing" OR "audience segmentation")
"Systematic reviews seek to collate all evidence that fits pre-specified eligibility criteria in order to address a specific research question. They aim to minimize bias by using explicit, systematic methods." (from Cochrane Handbook for Systematic Reviews of Interventions)
Use UC Library Search, the library catalog and more, to find books, reports, etc. on your topic. Books, while not often where original research is published, can often provide an overview of a topic and get you started with some key articles.