Behavioral rehearsal is a therapy technique in which behaviors, responses, and social skills are practiced and imagined being in use in order to prepare for when they will be used in reality. Think about a rehearsal for a play - the actors go through their lines and stage actions as if they were performing before the crowd on opening night. Behavioral rehearsal is a similar concept - a person can rehearse and practice behaviors and responses in order to be ready to use them in real life. Behavioral rehearsal is a way to improve social skills and interactions with other people.
There are different ways to do this. A person could simply imagine themselves in a social setting and picture themselves performing behaviors and responding appropriately. Other methods include role playing or talking about future behaviors and responses with another person.