Identifying a well-defined research question is the first step for writing a literature review. It should focus on something from the research field that needs to be explored, where there are gaps in the information. This will ensure that your contribution is valuable and that you are providing readers with a different angle or perspective on an issue or problem.
Your topic needs to be given careful consideration. A research question like “why are social networking sites harmful?” is too broad; there will be too much information to write a concise literature review. Change it to “how are online users experiencing or addressing privacy issues on Twitter and Facebook?" and it is more specific. It gives you a niche within the research field to focus on and explore.