Common Errors on APA References:
  1. First line flush left, all other lines indented 1/2 inch
  2. Double space references and space between references
  3. Authors should be alphabetized by 1st author
  4. No first names used for authors
  5. Place an ampersand (&) before the last author
  6. Article titles: words not capitalized, except for first word, proper nouns, and after a colon
  7. Journal name is italicized
  8. Volume number in italics, issue not in italics.
  9. Issue in parenthesis, no space between Volume and Issue.
  10. Page numbers not italicized.
  11. Do not use "Vol." "Issue" "pp.", etc.
  12. Punctuation:
    1. Comma after author's last name
    2. Period, Comma after Author's Initial
    3. Period after Year
    4. Period after article title
    5. Comma after journal name
    6. Comma after Volume (if no issue), otherwise comma after issue
    7. Dash between pages
    8. Period after pages.

Example:

Smith, B. & Crockett, D. (2004). Risk taking in adolescence: The effect of something on
         something else in American students. Developmental Psychology, 39(3), 1036-1046.


A good resource