I teach essay writing, and have found the following summary to be very helpful in getting students to think about their arguments:
Fundamentals for logical analysis
1. Always remember never to say always and never (and all and none, and everyone and nobody). Reasonable thinking should be reflected in reasonable language. All-inclusive statements can rarely be proved. Qualify and specify.
2. Even if you are sure that one thing is the cause of another, it may not be the only cause. Be careful not to oversimplify.
3. Suspicious words like “undoubtably” and “obviously” are often followed by hasty generalizations and oversimplifications.
4. Any opinion you have must be qualified and specified, and must be supported completely with facts, examples, or personal experience.
Joy M. Reid, The Process of Composition, p. 101 ff.