Your literature review should be guided by a central research question. Remember, it is not a collection of loosely related studies in a field but instead represents background and research developments related to a specific research question, interpreted and analyzed by you in a synthesized way.
How many studies do you need to look at? How comprehensive should it be? How many years should it cover? This may depend on your assignment. How many sources does the assignment require?
Make a list of the databases you will search. Remember to include comprehensive databases such as WorldCat and OneSearch, if you need to.