Your paper should be typed in 12-pt legible font (APA recommends Times New Roman), double-spaced.
Every page should have a header of the title of your paper, in all CAPS. On the title page, the header should include the words "Running head" before the header. The header should be the shortened title of your paper, not exceeding 50 characters.
Purdue OWL made a great video tutorial detailing proper APA paper formatting.
An example of APA formatted paper from Purdue OWL.
Every item on the References page MUST be used and cited in text of your paper.
The word References should appear on the very top line, on a new page, at the end of your paper, with the alignment set to center.
All lines after the first line in each entry must be indented by a half inch, known as the Hanging indent. Make sure that the entries are all double spaces. Here is a tutorial on setting up a hanging indent and double spacing for your References page.
List authors using last name first, followed by first and middle initials.
For multiple resources by the same author, list the entries in chronological order, from oldest to newest.
Make sure the journal titles look exactly as they are written in the journal.
Capitalize all major words in journal titles.
For article titles, chapters, and websites, capitalize only:
Journal and Book titles are italicized. Article titles, chapters and websites are not italicized, underlined or presented with quotation marks.