It is highly recommend that you collaborate with a librarian on developing your search strategy. Librarian are experts on identifying appropriate databases, developing comprehensive search strategies, writing the search methodology, and providing documentation for the line-by-line search strategies for use in the manuscript appendices.
According to the National Academies of Sciences, Engineering, Medicine: Standards for Systematic Reviews Standard 2.1.3, the review team should "include expertise in searching for relevant evidence".
Connecting terms with AND requires all terms to appear in the same article.
Connecting terms with OR results in articles that include one term, a combination of terms, or all of the terms.
Many databases allow you to filter your search. You can usually find filters are on the left-hand side of your results page. Based on your selection criteria, you may want to filter your results based on:
Searches should seek high sensitivity, which may result in relatively low precision.
More info: Higgins JPT, Green S (editors). Sensitivity versus precision (section 6.4.4) Cochrane Handbook for Systematic Reviews of Interventions. Version 5.1.0 [updated March 2011]. The Cochrane Collaboration. Available from http://handbook-5-1.cochrane.org. Accessed June 1, 2018.
If you're searching different databases for information, keep in mind that you may need to adjust your search terms for each database. For instance, the equivalent subject heading for "Heart, Artificial" in PubMed is "Heart, Mechanical" in CINAHL. Additionally, because CINAHL is an allied health and nursing database, you will find specialized subject headings such as "Toileting" in CINAHL that you won't find in PubMed.
Keywords are more likely to stay consistent across databases.