Look at your concepts or PICO statement again - are you very familiar with all of your concepts? Could you explain the concept to someone outside of the field? If not, then you need to do two things before starting your literature review:
For background information, you need resources that summarize the important points of a subject; these resources can be encyclopedias, upper level textbooks and handbooks (sometimes called manuals). For finding definitions, use dictionaries.
Two good sources for finding background information in engineering are:
Another source to try::
Where to look for science and engineering information depends on what type of information you are trying to find. Listed below are the different types of publications in which science and engineering information usually appears. Because journal articles and conference proceedings should be covered (note that the same resources are used to find both) the resources for finding these are listed first, followed by the remaining types in alpabetical order. Whether you need to be concerned with finding the other types of material will depend on your topic.
In addition to science and engineering information, you may also need: