When should I use other scholars' literary criticism in my essays and how should I go about it?

It is essential to explore the ideas and opinions of others in addition to your own when analysing texts. Regardless of intended audience, the vast majority of literature you come across will have been read by a huge variety of different people with different interpretations of the work, and when considering your own it is vital that you can make an effective and well-reasoned contribution. There are times, for example when completing a close-reading assignment, when it may be inappropriate to focus on criticism over careful study of the source material, however an awareness of the academic discussion surrounding a particular text will inevitably enhance your understanding and responses. Moreover, if an essay question asks for an extended discussion of a particular element of a text, you will find a great many ideas you can use to support, strengthen and expand your own argument in the work of literary critics and scholars.
When you are reading a text, make a note of anything you find interesting, difficult to understand, particularly effective or perhaps not so effective. When you are researching your essay, read some scholarly criticism and see how they approached what you have identified in your notes. Do you agree with what they have said? Or have they not convinced you of their interpretation? Most importantly, are you able to use your knowledge of the text to argue for a different way to think about its content? This way, when you are writing extended essays they do not become lengthy descriptions of a text, nor will they appear prejudiced, but they will be effectively argued pieces of academic discussion which take into account existing scholarship yet also make original contributions to the debate.