What is the general rule for forming the present subjunctive in French?

Firstly, take the present, third person plural conjugation of the verb, e.g. prendre > prennent, donner > donnent, finir > finissent. Next, subtract the 'ent' from the end, e.g. prennent > prenn, donnent > donn, finissent > finiss. Finally, add the following endings depending on whether the conjugation is in the first, second or third person, and whether it is singular or plural: Je : e. Tu : es. Il/elle : e. Nous : ions. Vous : iez. Ils/elles : ent.