If you're carrying out a thorough search for information to support your work, it's important that you are familiar with the most relevant databases and other sources.
Remember that all databases work a little differently. It's vital that you understand how the database you are using will interpret your search terms. Familiarise yourself with the help pages for the database, and make sure you understand the search rules.
UCL Library Skills have produced some guides for some of the well used database platforms (such as Ovid) and specfic databases (such as PubMed).