Imagine that the stage is divided up in to areas. When actors move on stage, it is referred to as "blocking." This concept is essential to understand stage directions. The back wall of the stage is referred to as "upstage." The lip or apron closest to the audience is "downstage." "Stage left" and "stage right" refer to the actor's left and right -- when he is facing the audience.
Use one or more directions when talking about the different blocks on stage during the play rehearsal. For example, you might say, "Should I move upstage?" or "Place the chair down right."
Recognize that "cross" means to traverse the stage completely, from one extreme to the other. The phrase "Hit your mark" calls on the actor to stand at a previously designated place on stage and say his lines.
Understand that some directors will simply tell an actor to move left or right and not specify stage left or stage right. It's OK to ask, until you are familiar with how the director works. Remember that even if you are facing upstage, stage right is now on your left side, and stage left on your right.
Understand that there are directions for the house also. The "house" is where the audience sits. "House left" and "house right" are audience members' left and right when they are facing the stage. The front of the house is the area of the audience closest to the stage, and the back of the house is the area furthest from the stage.
Use a pencil when writing down your blocking in your script. You may have to make changes as rehearsals go on. Underline the exact line when you are supposed to move and draw the line all the way to the left of the page and write in the blocking note.
Try creating shorthand for yourself, like "X DSL" for "Move down stage left," to help you save time writing during rehearsal.