There are four basic techniques you can use to improve your search skills:keyword, Boolean, phrase, and truncation searching.
All of these techniques can be used together to create precise searches.
When you combine keywords with AND you will only get results which contain all of the keywords joined by AND.
Use AND when you need to narrow a search to contain ALL keywords.
When you combine terms with OR you will get results which contain any of the terms joined by OR.
Use when you want to broaden a search to search for related terms or variant spellings (example: "climate OR climatic OR climates")
NOT is used to specify keywords to ignore. Some search engines and databases don't support NOT (Google uses "-" instead for example). NOT can be useful when you are searching for a word with multiple meanings or need to exclude certain topics from a search.
Phrase searching is, as its name implies, is best used if a phrase is wanting to be searched as opposed to distinct keywords. Personally, I use phrase searching more than any other strategy, and this extends beyond databases and is useful when searching using yahoo search, bing, or google. Phrase searching is accomplished by putting quotes around the words you would lke to be searched as a phrase. A few examples of phrase searching:
"ray shark" versus ray and shark
If you search ray and shark, there is a good chance that you will get articles that discuss both ray's and shark's. However, if you were searching for the animal called a "Ray Shark", then by using quotes you can ensure that all your results will be about Ray Sharks only and will not be about sting ray's.
"microbial ecology" versus microbial and ecology
By combining those two to search for the commonly used phrase "microbial ecology", you ensure that you are getting papers on that topic. If you used keyword searching for this situation, you would get a much broader range of topics, as you are not forcing the database or search engine to find that exact phrase to search.
Truncating is a good strategy to use for some terms, depending on the situation. Truncation is a way to search for the root of a word, thus greatly increasing the number of results on related terms. Exactly how to truncate is different for different databases, but often using either an asterisk* or question mark? is what will be required of you. Take a few seconds to check the help pages for truncation rules. For example..
microb* or microb? will give the following results:
microbe, microbial, microbiome, microbiology, microbolometer,etc...