“Etc.” is an abbreviation for the Latin phrase “et cetera” which literally means “and other things.” It is appropriately used when discussing various, similar things but not when discussing various, unrelated topics or things.
I do not believe the abbreviation “etc.” should be used in formal writing. I’m indifferent to the use of the full phrase “et cetera” in formal writing—I don’t personally use it, but I also don’t believe it is incorrect to use it in appropriate situations. If you do choose to use “etc.” or “et cetera,” follow these guidelines:
-The abbreviation “etc.” should always have a period.
-Do not precede “etc.” or “et cetera” with “and.” “Et” means “and.” Adding “and” is duplicative.
-Do not italicize “etc.” or “et cetera.”
-“Etc.” or “et cetera” should always be preceded by a comma.
-“Etc.” and “et cetera” should not be used when speaking of persons. The lawyer’s favorite, “et al.,” is appropriate in that situation.
-Use one and only one “etc.” at the end of a list.
Consider the following appropriate uses of "etc.":
To prepare for our trip, please pack toiletries, cosmetics, clothes, etc.
My favorite books, A Hundred Years of Solitude, The World According to Garp, etc., have influenced my writing style.
My favorite authors, Garcia Marquez, Irving, et al., have influenced my writing style.