I have a job interview tomorrow, I need to prepare.
'Colloquio' — col-LO-quio. Stress on the second syllable. Four syllables.
Use when a job interview requires preparation and you need to cancel evening plans. This reason generates both understanding and genuine good wishes from Italian friends.
'Colloquio di lavoro' is the standard Italian term for a job interview (not 'intervista' which means a journalistic interview). 'Devo prepararmi' (I need to prepare myself) shows the interview is important to you.
Devo prepararmi per un esame.
I need to prepare for an exam.
For students — studying for an exam is highly respected as a reason to cancel
Ho una presentazione importante domani.
I have an important presentation tomorrow.
Professional context — generates respect and understanding
Devo ripassare per il lavoro.
I need to review/revise for work.
'Ripassare' means to review or go over material — common student/professional phrase
'In bocca al lupo' (into the wolf's mouth) is the standard Italian way to wish someone luck, used before exams, performances, and interviews. The correct response is always 'crepi!' (may it die!) — never 'grazie'.