Use the citation style your Professor recommends.
Each major citation style (MLA, APA, Chicago) will include common legal resources. See the Middlebury Citation & Style Guide for help.
Use the legal-specific citation guides (Bluebook, etc.) to help you decipher legal citations you encounter or for examples of more specialized resources not adequately covered by the major citation styles.
Middlebury's Citation & Style Guide (go/citations) provides links to the major style guides and provides examples of the most common types of citations. It also has links to citation software that will help you store, take notes, and cite your sources. The top tools (Zotero & Refworks) to store and format citations are listed here as well.