With a student, I would first discuss with them what the already know about the subjunctive, or any phrases they already feel happy to use in their written or oral work. We would then discuss the fact that it is simply necessary to learn the conjugations of the verbs. Although the subjunctive of many verbs is identical to their usual conjugation, many other verbs can be quite irregular. We would go over the main irregular verbs, and their subjunctive conjugations. 'Je suis' becomes 'je sois'; 'je peux' becomes 'je puisse'; 'je fais' becomes 'je fasse'; 'j'ai' becomes 'j'aie', and so on. Together, we would then go over the various uses of the subjunctive (emotions, commands, advice, opinion, possibility, doubt, negatives, etc) and construct example sentences for each use of these uses.