You must be absolutely sure that you know, as precisely as possible, what your topic is. If you are thinking of several related ideas, and cannot choose, then sit down with a document and jot down the good and bad points of each. Then, before you begin researching, decide on precisely what it is you are looking for; reading, without a clear idea of what you are looking for, is ineffective and daunting.
Once you have decided on an area of research, ask your tutor for guidance: ‘If you were researching this topic, sir/madam, then what books or articles would you consider essential?’ Your tutor is there to guide your study, and they have a huge amount of experience and reading behind them.
A basic online search, even, though definitely NOT limited to! Wikipedia, will show you the main trends and the main thinkers in a particular area. You can also, through this kind of research, find references to the key texts.
Most topics or areas of study have ‘seminal works’. A seminal work is a piece of writing or research that is seen as being essential in any discussion of that topic. For example, when we write about what it means to be an author, we almost always have to reference ‘The Death of the Author’ by Roland Barthes. These show that you understand your field. Also, in finding one or two key texts, you can find other sources: ‘A is important, but A says that B is equally important’.
Follow up on references found in the key texts that you have discovered. The bibliography in any study will be a list of names and works that will be relevant to your field. If you were examining consciousness for example, a book by Antonio Damasio will have a bibliography of texts that are helpful. Always make a note of, and research, frequently occurring names, as these are likely to be the important people in this field.
In every page you read, make sure that at the front of your mind is your topic. You need to keep asking: ‘Why am I reading this? What am I looking to evidence?’