A good way to find the meaning of a quote is to research it in a book such as "Bartlett’s Familiar Quotations," by John R. Bartlett, or "The Oxford Dictionary of English Idioms," edited by John Ayto. Websites such as idioms.thefreedictionary.com and idiomeanings.com are also good sources.
"Bartlett's," first published in 1855, arranges the quotations by author, instead of the letter, and arranges authors chronologically by date of birth, rather than alphabetically. Within each year, the editors arrange authors by alphabet and the arrange quotes chronologically. A well-planned and thorough keyword index details the source of each quote. Bartlett's is now available in the Apple iStore as an app for OS and Nook.
Another source similar to Bartlett’s but with more concentration on American quotations is the Yale Book of Quotations, edited by Fred R. Shapiro. The Oxford Dictionary of English Idioms, edited by John Ayto and The Dictionary of Idioms and Their Origins by Linda and Roger Flavell are two sources that make it a point of defining what a quotation such as “mind your p's and q's” means.
Some websites that are also helpful in looking up quotations and phrases are phrases.org.uk, which lets the user search quotes based on their first letter, idiomeanings.com, idioms.thefreedictionary.com and idiomsite.com.