Remember, literature searching is a combination of an art and a science. It requires practice, intuition, and some trial and error. While there is a basic structure, a set of guidelines and many tools for assisting one with basic searches, there are a variety of nuances and advanced techniques that may be required for more specialized searches. (from "Conducting a winning literature search," Erika D. Ecker and Andrea C. Skelly)
Digital Health Evidence provides its results by executing searches against the PubMed database, so the rules for constructing a good Digital Health Evidence search are the same as those for constructing a good PubMed search. For guidance on how to approach your search and develop your query see Conducting a winning literature search.
One specific tip for refining results that you may notice behind many of the "Quick Searches" is the use "boolean logic":
Add terms or combine search terms with connector words: AND, OR, or NOT using upper case letters (called Boolean logic)
More advanced searching can be conducted using Medical Subject Headings or "MeSH" terms:
For example, the query behind the "Quick search" for Governance uses the MeSH terms "public policy," "health planning" and "legislation as topic":