Final answer:
The sentence given is already correct and does not require any changes. It indicates a sequence in which an actor walks out onto the stage before speaking. Additionally, standard stage directions are based on the actor's perspective relative to the audience and distinguished in writing by being italicized.
Step-by-step explanation:
The sentence 'Before the actor spoke, he walked out onto the stage' is already grammatically correct. In this sentence, the actor is preparing to address the audience, which means that his action of walking onto the stage occurred prior to speaking. The sequence of events is clearly outlined, with him first making his physical appearance by walking out onto the stage. Proper stage direction terminology indicates that if the actor should approach the audience, it would be termed as 'coming downstage,' and if moving away, 'walking upstage.' These directions are based on the actor’s point of view while facing the audience, with his back to the rear of the theatre. Furthermore, stage directions often found within a script are typically italicized to differentiate from the dialogue, something that is evident in the provided sample.