How do you conjugate the present subjunctive mode?

For regular verbs, these conjugations are relatively easy - the way I remember it is that you switch the endings of AR verbs with those of ER/IR verbs in the indicative.

e.g. present indicative comer: yo como, tú comes, él come, nosotros comemos, vosotros coméis, ellos comen

present indicative bailar: yo bailo, tú bailas, él baila, nosotros bailamos, vosotros bailáis, ellos bailan

So to conjugate comer in the present subjunctive mode, we put the endings from bailar onto the stem 'com' (except in the first person singular).

e.g. yo coma, tú comas, él coma, nosotros comamos, vosotros comáis, ellos coman

Irregulars you just have to memorise but they all have the same endings as above, it's only the stem that changes.