All tenses
Present, perfect, simple past, pluperfect, future, Konjunktiv I + II.
Present, perfect, simple past, subjunctive: all tenses, all persons, all moods. Until you no longer have to think about them and simply say them.
Present, perfect, simple past, pluperfect, future, Konjunktiv I + II.
Sein, haben, gehen, kommen: drill the 80 most important irregular verbs.
Conjugate against the clock until it becomes muscle memory.