Use Controlled Vocabularies
Many databases use specific terms that are used to "tag" articles to describe or categorize or classify what the article is about. These terms are also called Subject Headings, Thesaurus, etc. Find these terms and combine them with your search terms for your topic of interest. For example:
In PubMed, combine your search term for the topic of interest with "Qualitative Research"[Mesh] using the Boolean operator AND
In CINAHL, combine your search term for the topic of interest with (MH "Qualitative Studies+") using the Boolean operator AND
Use Keyword Search Terms
Qualitative articles have some common words that are frequently used. Combine these keyword search terms with your search terms for your topic of interest. Here is a possible keyword search strategy to combine with your search terms:
(qualitative OR ethnograph* OR phenomenol* OR ethnonurs* OR grounded theor* OR purposive sampl* OR hermeneutic* OR heuristic* OR semiotics OR lived experience* OR narrative* OR life experience* OR cluster sample OR action research OR observational method OR content analysis OR thematic analysis OR constant comparative method OR field stud* OR theoretical sample OR discourse analysis OR focus group* OR ethnological research OR ethnomethodolog* OR interview*)
There are many more possible terms, and those terms will depend on your qualitative research question.
Use Database Filters/Limits
Many databases will provide a filter or limit to focus your search results to only qualitative research. Typically these options will be in the Advanced Search function or show up as filters/limits after you have run your search on the topic of interest.
See "Finding Qualitative Research Articles" from the University of Washington Health Sciences Library.