The English Faculty does not prescribe one referencing method but its advice is to be consistent, so pick one and stick with it! Your tutor can help advise which method to use. You will find brief MHRA guidelines in the FHS handbook which also includes basic instructions and clear advice.
You can download the MHRA Style Guide or take a look at the few Style Guides held in the Reference section of the Library!
The University has produced a short guide to what constitutes plagiarism, and how to avoid it.
You can also find a useful annotated guide to some of the more common types of unoriginal work in this guide created by Turnitin: http://turnitin.com/assets/en_us/media/plagiarism_spectrum.php
RefWorks is an online research management tool that will let you - amongst other things - generate citations and bibliographies.
The Bodleian Libraries has a subscription to RefWorks, so any member of the University can create an account.
N.B. If you want to access your account from outside the Oxford domain, you will need to input the Oxford "Group Code" before being presented with the RefWorks login page. You can access the Group Code here using your Oxford University SSO username and password.