Blocking is another word for the movement and choreography of a play. The director's job is not only to help actors with dialogue and motivation, but also with how the actors move and enter and exit each scene.
Learn the terms: center stage, stage right, stage left, up stage and down stage. This is the vocabulary a director uses when blocking a show. Stage right refers to the actor's right and stage left refers to the actor's left. Up stage is towards the back wall of the theater and down stage is towards the audience.
Consider the general rule of thumb that characters must not remain in one place for more than 2 pages of dialogue. They must cross from one side of the stage to the other or at least move from their current position.
Make sure the actors are not being blocked by one another and that the actor's mouth is facing down stage. The director paints a visual picture through the blocking, yet keep in mind that the actors need to be seen and heard.
Keep in mind that a character must have a reason or motivation to move to a new place. The blocking should look natural for the character and should complement the dialogue.
Many directors draw out the blocking on paper before the rehearsals.
Make sure your actors write down their blocking in their script. They must memorize this along with their lines. If you don’t like the way you blocked something, change it. That's what rehearsals are for.