Authority: Provide evidence for your statements
Clarity: Make it easy for your reader to find the sources you’ve used
Credibility: Show your reader the range of resources you’ve consulted
Persuasion: provide evidence from reliable sources to strengthen your case
Avoid plagiarism: correct referencing is an important academic skill to acquire
Statements of law: cite the relevant case or statute
Direct quotation: attribute the source where you found it: a book, article, case, or other
Facts: cite the source of any statistics or research data. If a fact is common knowledge, no need to reference it.
Definitions: cite the dictionary, case or statute where the term is defined
Common knowledge: If the information can be found in numerous places and is known by many people, it is probably common knowledge, so there is no need to footnote it.
If you use your own words to express an idea that is specific to a particular writer (a judge in a case, an opinion in a book), cite that source even if you explain the idea in your own words. But, if you have read several textbooks to get an overview of the topic and the same idea is expressed in each one, then you may not need a specific reference when expressing this idea in your own words, because information that is widely known may be considered "common knowledge".
When in doubt, reference it.
Statements of law should be attributed to an authoritative source, such as the relevant Act, case, regulation, or rule. These are primary sources. For interpretations of the law, you can also cite secondary sources, such as legal encyclopaedias, government documents, Parliamentary reports, law Journals and textbooks.
Beware of free law sources that you find on the Internet. Some of these may provide inaccurate legal advice, as mentioned in this article from The Guardian.