Write down what you know about the topic and questions you have about it. You can use concept maps to help you and to generate keywords you can use in your search.
We often use different words to describe the same concept. Developing a list of keywords about your topic can be useful when searching.
For example, "global warming" and "climate change" are both useful search terms for that topic.
When searching library databases avoid asking long questions, save those for Google. Try selecting keywords from your research questions, thesis, or concepts maps.