Prompting is one of those vital jobs that the audience often overlook (provided that you're not needed). Prompting is an enjoyable task which could even help you decide whether you wish to remain backstage or appear on stage. If you like reading and are interested in watching a play from a different angle (usually through a small gap about waist height at the front corner at the side of the stage), then this is the job for you.
During early rehearsals you have the opportunity to sit back and watch where the actors move and when they pause whilst reading from their scripts. As rehearsals progress, you mark up your own copy of the script to help you find your way round a page quickly (for example, entrance and exit cues, moves and so on). The fun really starts when the producer decides to dispense with the scripts - the cast (some more than others) will rely heavily on you. You have the choice of simply offering a word or two if they stop or having a quiet word afterwards to remind them which bits to look at, especially if they keep getting caught by the same phrases.
So far, so good. An added complication occurs during later rehearsals when the backstage crew turn up and tell you that you will have to move from that comfortable chair with a good view of the stage to a dark corner where, using a torch to follow the script, you will have to kneel and peer through a small hole to see the action.
Prompting during a performance (hopefully you won't be needed) requires you to speak at a pitch and volume that the suffering actor will hear, without your voice reaching the back row of the auditorium. You also require judgement - not giving enough of the phrase leaves another embarrassing silence whereas too much results in two people speaking at the same time.
If you think you can do this then come along to any rehearsal (most Tuesday and Thursday evenings starting at 8:00pm) and find out more.