In regular theater an actor may prepare a monologue that he has spent many hours memorizing, for a part that he will also perform at every audition. He’s spent a lot of time on this and has perfected his art and delivery. When going for an audition he is quite comfortable with his prepared lines. However, in a film or commercial audition the actor is expected to perform a script given to him that he has never seen before. This is when the art of cold reading is very important and can be a life saver.
The technical definition of cold reading is the auditioning for a part with a script in hand, one the actor has never seen. The profession says that the actor is supposed to be given the script at least 24 hours before the audition but all too often this just doesn’t happen. This is why cold reading is so important to actors who work in film or commercials.
So, how do you learn to cold read? Brute force. Pick up a script, read the first line, commit it to memory and then say the line without looking at the script. You’ve just done your first cold reading. At first you may only be able to memorize a few words at a time, but with a little practice...