A few tips on writing

Introduction: Make sure you have a short, clear introductory paragraph that lets the reader know what the paper is going to be about.
Genitive ['s]: "My mother's [not mothers] decision was difficult."
Its vs. It's: For example, "Its [not It's] most attractive feature is the price"
Gender-neutral language: To avoid the traditional sexist use of "he," use one or more of the following strategies: (a) alternate references to male and female (e.g., if you gave one example about a woman in one paragraph, use an example about a man in the next paragraph); (a) say "his or her" and "he or she" (but don't use the clumsy his/her or s/he); (c) use the plural form "people" (but don't say "they" if you refer to a single person).
A colon [:] introduces a closely related sentence part (e.g., "He made one major mistake: not to calculate the probabilities right"). The part after the colon can be a complete or an incomplete sentence.
A semicolon [;] separates two sentence parts more distinctly than a comma does and less distinctly than a period ("He was not tired; he was exhausted"). The part after the semicolon must be a complete sentence.
Plural words: "Phenomena" is a plural world--its singular is "phenomenon" ("These phenomena are intriguing"). The same holds for "data," which is the plural of "datum" ("The data do not confirm the hypothesis") and "criteria," which is the plural of "criterion" ("The criteria were set too high").
No definite articles for theories: "Dissonance theory predicts that ..." (NOT: "The dissonance theory") Same for attribution theory, signal detection theory, expected utility theory, prospect theory, etc. Note, however, that psychological processes or phenomena often do carry a definite article (the fundamental attribution error, the availability heuristic, etc.)