One of the most important things to keep in mind when using any type of search engine, from Google to academic databases, is that search engines don't understand the meaning of language or comprehend your intentions - they simply search for the words you enter. For that reason, choosing good search terms and building good searches is the best way to ensure a successful search.
Here are a few strategies that can make your search more effective:
It can be helpful to state your information need as a question or phrase, then break it down to the most basic forms of your keywords and concepts and, if necessary, identify possible synonyms.
For example: Environmental effects of fracking in North Dakota would be:
North Dakota AND fracking AND environmental
Possible synonyms for these terms might include hydraulic fracturing for fracking, and ecological for environmental.
It won't be necessary to include a version of effects in your search terms, since articles about fracking and the environment in North Dakota are already likely to discuss the effects.
The Advanced Search screen available in most databases provides you with a number of features to help you fine tune your search.
You can usually find the link to the Advanced Search screen below the main search box.