Basic Principle: A pronoun usually refers to something earlier in the text (its antecedent) and must agree in number — singular/plural — with the thing to which it refers.

   All About Pronouns

Which Hunt
If you wish to write naturally, don’t fuss too much about the usage of that versus which. Obsessive correction (what has sarcastically been called a “which hunt”) is best avoided. If your sense of the language is not strong enough to be sure of the right pronoun, use that for the restrictive cases and which for the others and you won’t go wrong.

Pronouns and Pronoun- Antecedent Agreement
The basics – artfully explained.

Pronoun References: Part I – When No Substitutes Will Do by K.K. DuVivier, 25 The Colorado Lawyer 29 (July 1996)
Ambiguous pronoun references plague much legal writing. Read about how to fix these problems.

Pronoun References: Part II - A Case for Pronouns by K.K. DuVivier, 25 The Colorado Lawyer 29 (September 1996) Five pronoun problem areas that arise in legal writing and what to do about them.

Gender-Free Legal Writing – Managing The Personal Pronouns by Arthur L. Close, Q.C.. British Columbia Law Institute, 1998
Having a difficult time with her/him and other awkward ways around pronouns? Check out this gender-free style of writing - one that avoids the pronouns entirely. This manual explores a number of techniques that you may use to create documents that are free of gender-specific pronouns. A terrific guide with plenty of examples of text revised to a gender free style.

Exercises
Forms of Who

That and Which

Pronoun Usage

Pronoun Forms

 

Usage & Grammar

Subject-Verb Agreement

Pronoun References

Apostrophes

Commas

Colons & Semi-Colons

Spelling

Words that Sound Alike

Capitalization