If you're going to be submitting articles to APA journals you should have access to the APA Publication Manual 6th edition. And it is useful to use a template (see here for discussion of 6th edition LaTeX packages) and a citation system that supports the rules.
There are changes that permit new things (e.g., longer abstracts, bullet lists, and keywords are permitted, single-spaced tables) and there are new suggestions (e.g., stronger encouragement to report confidence intervals; you can say "subjects" if you want; "I" and "we" are recommended over "the researchers").
However, if you already know the 5th edition, then changes of particular interest are those where compliance with the 5th edition would actually lead to violation of 6th edition rules.
Changes that stood out to me:
- Provide two spaces at the end of sentences (but this doesn't make much sense if you use LaTeX)
- Formatting of headings have changed and are simplified so that five-heading papers have the same first four headings as four-heading papers
- Figure captions are now placed on the same page as the figure below the figure.
- Tables and figures now appear before appendices
- Footnotes are now placed on the same page that they are referenced.
- Report p-values to two or three decimal places exactly and those less than .001 as
References changes that stood out to me:
- Include city and state for book publishers even if city is well known
- Provide DOI with any references that have a DOI
General summaries of changes from 5th to 6th edition
Of course there are lots of little changes, check out some of these references for some other reviews of changes and resources:
- Hughes, G., Onwuegbuzie, A., Daniel, L., and Slate, J. (2010).
Editorial: Apa publication manual changes: Impacts on research reporting
in the social sciences. Research in the Schools, 17(1). PDF