As you get started with your initial research, think about your topic of interest and create a set of keywords that you can use in searching. A good resource to help with this process is the thesaurus included in many online databases. Compendex from Engineering Village has a good comprehensive one: select the thesaurus tab at the top of the page to begin searching.
Keep adding to this list as you continue your research: when you find an article or abstract that relates to your topic, take a few moments to look at the terms it uses for your concepts. If there are new ways of stating the concepts, add them to the list to ensure that your literature searches will be comprehensive.
Trial and Error
Remember that no matter how well you know your field (or how familiar you are with the resources you are using) trial and error is a major part of this process. If your initial searches find too many results, either combine multiple keywords with and between them or try to think of ways to make your terms more specific and precise. If you initial searches find too few results, think of ways to make your terms more general, or combine similar concepts using OR.