You will get better results if you keep these things in mind:
- Use terms that are specific to your topic and only those terms. It is inefficient to use free text entry when only one or two terms will do.
- If you expect a word pair to occur together, define the terms as a phrase. This will retrieve only the documents in which the terms appear in exactly that sequence. With Google you can use double quotes such as "herald patch" and retrieve links that focus on pityriasis rosea while avoinding links to newspapers.
- Specify the domain of the search results. Using Google, type: fibromyalgia and site:.gov or "insulin pump" site:diabetes.org
- Get comfortable with one or two search engines and become familiar with some of the more advanced search techniques to help narrow your search.