A friend who read the Fallacy Files posts asked me to recommend an introductory logic textbook. The classic textbook is Introduction to Logic by Copi and Cohen. The fact that it’s now in its 13th edition is an indicator of its popularity and success. One of its best features is its extensive use of real-life illustrations of arguments and fallacies. It’s on the expensive side, admittedly, but it’s worth the investment if you’re serious about learning logic. You can probably pick up a second-hand copy for a tolerable price. It’s not crucial to have the latest edition unless you’ll be using it alongside others in a logic class.
All that said, Copi and Cohen can seem a bit daunting as a first port of call (even if it’s not a book one has to read from cover to cover to benefit from). A cheaper and more readable alternative introduction to logic is Come, Let Us Reason by Norman Geisler and Ronald Brooks. On the plus side, it’s considerably more digestible, and if you’re a Christian, you’ll appreciate the illustrations drawn from theology and apologetics. (If you’re not a Christian, you’ll most likely be irritated by it; by far the best solution in that case would be to become a Christian before reading it.) On the minus side, it suffers from too great a deference to Aristotelian syllogistic logic, and the examples drawn from theology often reflect the authors’ own biases (as one would expect). Still, no great harm is caused by either of these, and the book remains a reliable introduction to the basic concepts of logic: arguments, inferences, deduction, induction, formal and informal fallacies, etc.
There are also myriad online resources devoted to logic and critical thinking. I could list a dozen worthwhile ones here, but that would just invite the response, “Thanks, but where should I start?” My answer to that question would be to check out this excellent site (and work through the modules in sequence).
Of course, a mastery of logic, however valuable, is not sufficient on its own to win an argument (and cynics would say it isn’t necessary either). If you’re only interested in winning arguments, logic or no logic, these practical tips will serve you very well.
Footnote: There’s still a need for a distinctively Christian introduction to logic that not only provides a reliable guide to modern formal logic (as per ‘secular’ textbooks) but also opens with a discussion of the study and use of logic within the context of a Christian worldview. As far as the latter goes, the best I’ve come across is chapter 8 of John Frame’s The Doctrine of the Knowledge of God.