These will identify my proof-reading marks on your paper.  They are a short synopsis of common errors but don't substitute for the APA style manual.  Good summaries of APA style and other writing resources are in the Anderson Research Center.

In general, shoot for simplicity, and ignore anything you've read in a Kenneth Burke seminar as a writing sample.  The more complex the idea is that you are trying to express, the more simple the sentence structure and language you should employ.  Shoot for simple, declarative sentences.  The number one problem in collegiate writing (other than comma proliferation, see #8) is trying to sound too smart and making really confusing sentences.

And, duh, make sure you outline your paper.  Each paragraph should have a thesis sentence.  There should be a good logical flow from one paragraph to the next.  Treat the paper like a speech:  Preview what you are going to do, clearly mark each separate idea with a transition, and review each section.  Sounds easy, but it makes a big difference.

1) If you use a direct quote, you need to include page numbers.  Example:

According to Gass, "The Lakers can't win unless Shaq can hit free throws" (p. 121).

2) Subject/verb agreement.  Subjects and verbs are plural, if you have a plural subject you need a plural verb.

Bad example: The Dodgers is worse than the Angels.  ("Dodgers" is a plural subject but "is" is a singular verb)

3) Awkward sentence:  The sentence doesn't necessarily have a grammatical error (although it might), but the writing is failing to express an idea clearly.  This usually happens because too many ideas are packed into a single sentence.  Try to break the ideas up into several smaller, simpler sentences.

4) If you are citing multiple authors in a parenthetical reference, you should list them alphabetically.

Bad Example: (Gass, 2000; Bruschke, 1999; Gudykunst, 1832)

Correct: (Bruschke, 1999; Gass, 2000; Gudykunst, 1832).

5) Tense shift:  Write in either the past, present, or future tense.  Do NOT shift tense within sentences, paragraphs, or sections.

6) Punctuation ALWAYS falls INSIDE quotation marks.  The British do it differently, but they keep losing World Wars we have to bail them out of, so who cares what they think?

Bad Example:  The inability to shoot free throws is called "Shaqitis".

Correct: The inability to shoot free throws is called "Shaqitis."

7) Do NOT use back-to-back parentheses; use a semi-colon instead.

Bad Example: Raider fans are the lowest-rated human in terms of Intelligence Quotient (IQ) (Jones, 2001).

Correct: Raider fans are the lowest-rated human in terms of Intelligence Quotient ("IQ;" Jones, 2001).

8) Comma splice.  If there is one problem that college students have it is the overuse of commas.  Find and kill them.  Treat them like dentist visits -- useful when it must be called upon, but definitely something you don't want to use more than you have to.  Technically, a comma splice is separating the subject and verb of a sentence with a comma.  You can fix almost all of them but cutting your comma use to the bare minimum.

9) If you are citing multiple pages use 2 ps, not one.

Bad example: According to Gass, "The Lakers can't win unless Shaq can hit free throws" (p. 121-122).

Correct: According to Gass, "The Lakers can't win unless Shaq can hit free throws" (pp. 121-122).

10) You have cited something in the text that isn't in the reference list.  Add it to the reference list.

11) Do NOT use the royal "we."  You almost always mean "scholars," "society in general," or "the author and reader working together as an intimate collaborative."  The latter is especially irritating because its really the writer who's doing everything.  If by "we" you mean the reader and writer, use the first-person "I" instead.  If you mean "scholars" or "society" just say so.

12) Spacing error:  Either you don't have one where you should or you have one where you shouldn't.  DO put a space between the period and page number (p. 123, NOT p.123), DO put a space between all terms in statistical copy (n = 121, NOT n=121).  Also, check your indents.

13) In-text reference error.  DO NOT put any punctuation before the parentheses, like this. (Gass, 2001).  Do it like this (Gass, 2001).

14) Avoid "as cited in."  Seriously, this almost always means "I'm padding my reference list."  The best solution is to look up the original citation and quote it directly.  If you can't do that, just say so in the text.

Bad example:  Johnson reports self-disclosure has been found to be annoying when conducted by Dodger fans (as cited in Gass, 2001).

Better: In Gass' (2001) discussion, he reports research by Johnson that points to the conclusion that Dodger fans have annoying self-disclosure.

15) If you are starting a sentence with a number, write it out alphabetically.

Bad:  34 people were surveyed.

Good: Thirty-four people were surveyed.

16) Effect vs. affect.  "Effect" is a noun, "affect" is a verb.  "Affective" usually means "emotional."  If you are talking about how well something works, use "effective."