Step one of the lesson should describe the subjunctive mood which, according to "St. Martin's Handbook," expresses wishes contrary to facts; it is the "what if" attitude of a writer: "If I had done the right thing, I would not regret the past." Students should realize that the subjunctive mood is one of three moods in English, the others being indicative (used for facts) and imperative (used for commands). Since the subjunctive mood expresses requests or desires, it causes the most problems with tense.
In step two, students should be reminded that the base form of the verb -- such as "be" or "drive" -- is always used in subjunctive mood, as in "It is vital that you be" -- not are -- "prepared for this" and "We ask that she drive" -- not drives -- "more slowly." Also, the only "to be" past tense used is "were," not "was": "If I were you ..." Once these two ideas are mastered, it's easy to create subjunctive adverbial clauses, which add specificity to the wish or desire.
In step three, teachers should give numerous examples. A subjunctive "why" adverbial clause would be "'If Bill could drive the Mercedes, Jane might notice him." The sentence's main action is Jane noticing Bill; the subjunctive adverbial clause addresses why he might do so. A "when" example is "If you let Bill drive the Mercedes, Mom's gonna throw a fit." A "where" example is "If Bill should drive the Mercedes to the country club, he better return it without a scratch;" a conditional example is "If Bill were to drive the Mercedes fast, he'd get a ticket."
Subjunctive and adverbial examples in past tense include "If I were to rest, they'd all stop working," "If I were to get up now, I'd be very sleepy" and "If they were to repeat the drill, the coach would be satisfied." Remind students that the purpose of each clause is to combine a promise, wish or conditional event with the specifics of why, when, where or how it may be fulfilled.