When trying to generate a feeling, many actors will think about a time in their life when they felt the way their character is feeling. For example, if an actor had a dog that they had to put down because it had cancer, the thought can create an emotion, which can affect the quality of the performance. The actor's empathy toward the dog that was put down will create the necessary emotion.
Actors can use their real-life relationships to transform their performances by generating authentic emotions. An actor thinks about a person for whom they feel empathy. They get as specific as possible and think about why they feel empathy for that person. Actors also dedicate their performance to someone they love. This can sometimes give the actor a reason to perform and their mind becomes focused on how they are conveying the character.
By watching the news, actors generate a wide range of emotions, whether it is the feeling of anger about people dieing in war-torn countries or love about a person who raised money to help fight cancer. Actors who think about people starving in Angola can feel empathy, for example. Before the camera starts rolling, the actor concentrates on the suffering and harnesses the emotion, releasing it when the director calls "action."
Each actor has a way of generating emotions, but they all train the key concepts to find which technique works best in a scene. Many actors begin their training through improvisation. The technique allows each actor to practice emotion generation without the need to worry about their lines. Each actor is trained to focus on generating an emotion and then reacting to the behavior of fellow actors.