The relationship between researching a university essay and writing it is not a straightforward sequence of first finding out bits of information or facts which your writing will then simply "present". This way of thinking about research reflects a basically writer-orientated perspective in which the significance of the information is assumed to be obvious, whereas from the reader-orientated perspective which is required by the expectations of work at university level, defining the problem is a central component of the research process.
There is a chicken-and-egg problem here. You can't adequately define the problem posed by an essay until you have developed through research an understanding of the academic field to which the question relates, and yet once you have found an angle on the question you will probably need to go back and do further research on the specific topics you have decided your essay is going to cover, something which will require a more directed and selective approach towards searching for useful sources. In this way, the writing and the researching processes will feed off each other, in a way that your note-taking should reflect. In the early stages, when you are orientating yourself in the academic field, your notes will be less detailed than when you are looking for supporting material for an argument you have already defined.
Since a university essay doesn't simply present facts, but sets out a synthesis by providing motivation for the pieces of information it contains through relating them to an overall argument, you need to be clear about the status of the sources you use. This is not simply a matter of the reliability of the information they contain, but of the degree of authority they possess.
Choosing which sources to use also requires some consideration of the nature of the academic field to which your subject belongs - if you were working on a novelist whose books had mostly been published after the year 2000, it might be acceptable to use reviews in newspapers or on the web as references, in a way which would not be appropriate to an essay on Charlotte Bronte, where there are many authoritative academic sources to be used. These considerations about how well-established the topic is as an area of study will also affect how you choose to search for material - academic bibliographies, for example, do not normally include items published in newspapers and magazines.