1. Brainstorm keywords that are associated with your topic/project. Identify key concepts and terms, and think of related words and synonyms that you might also search. Gather background information about the organization you are working with, and the types of work they do. Think about broader terms that encompass your main ideas, as well as more narrow related terms that could be generalized to your project.
2. Try some searching. Are you finding too much or too little? Consider whether you need to broaden or narrow your topic to get better results. Finding good results? Check the subject terms used in your best sources, and then use those to find additional sources.
3. Use citations/references listed by relevant articles to find related articles. Google Scholar can be used to find articles citing one you already have (search for your article then click "cited by" under the result). This gives you articles that are more recent than the one you searched.