Improv is a standard first step for actors because it gets the actor comfortable performing. The actors either create their own premise for a scene or they are given one by an instructor. For example, the scene theme can be "conflict," and the actors develop characters and improvise. The actors are trained to listen to their partners, to roll with what is said, to further their character and to develop the scene. Improv teaches the actors to work with a variety of costars, and to feel the dynamic between the characters.
A fundamental component of becoming a successful actor is being adept at the audition. Without being comfortable, confident and sharp when matched up against dozens or hundreds of other actors, performer will never land a role. Reviewing your work while on camera is an important component of seeing how you behave when being filmed during a mock audition. Instructors and peers can help point out your strengths and weaknesses, as few actors are able to objectively judge their own work.
Often in an audition you will be given your lines upon arrival. You then have some time, usually 15 minutes, to review the character and lines before delivering at the audition. Actors train for this ahead of time to become skilled at memorization and quick character development. Acting students are put through a mock audition before delivering their lines on camera. They are taught about acting naturally and drawing on past experiences to make line delivery more natural.
When not practicing improv or cold reads, actors are given more time to develop the nuances of their character. Each actor has her own style to address the character, but many will read through the script first, while taking notes. Flashes of the character might appear in her head, and she can document qualities that her character possesses. Many actors draw on people who they know to base the character around, or concepts, such as Johnny Depp in "Charlie and the Chocolate Factory," when he added a children's show host and a game show host element to his portrayal of Charlie.