Knowing how many different voices you are going to hear will help you prepare before you listen to the text. There is sometimes information in the question which will give you an idea of who is speaking, and you can start to imagine the scenario.
How many speakers are there? Look at the instructions. Is it a dialogue? A monologue?
Is it an interview? If so, the interviewer's questions may be the same as your questions. This will help you listen for the answer.