Take some graph paper and draw yourself the outline of a stage. Include a door, a chair and a platform. Now draw some lines connecting the door to the chair, then from the chair to the platform, and then towards the door again. This simple exercise illustrates a vital component of scenography, which is that the scenery is not placed in an otherwise empty space but is placed in a space occupied by a person who has to cross the stage, turn around, stand still, hold something or remain visible while the scene takes place.
A set might look fine on a simple front view drawing but fall apart in the presence of movement. A large platform might make a great silhouette but stop anyone from entering through the most obvious entrance. A chair that looks right in the centre could demand awkward movements to get around it. Two flats next to each other might appear to leave enough room in theory, but not actually have enough space for a human being wearing a costume and carrying a prop. Good stage design therefore needs to be combined with blocking and movements paths as well as the composition itself.
Think about the movements required by the play rather than the placement of the set first of all. Identify where the entrances and exits are, where things are said and done and if any characters sit, hide, go up stairs, open doors or run. Put some lines onto the floor plan representing these movements. You do not need to show the movements to be used in a fully produced show. Rather, you need to see if your scenographic concept leaves enough room to choose from or if several movements are competing for a narrow space.
Not every part of the stage needs to be used. The empty space between one set of actions and another might carry meaning itself. Two people sitting on opposite sides of the stage creates a different stage picture to two people sitting on opposite sides of a table between them. The space down centre of the stage might help you focus on a crucial battle. A set which fills the entire stage might make movement and clarity more difficult.
Sometimes it is difficult to know exactly what size something needs to be and you can end up with problems that make the movements harder rather than easier to execute. A door, a staircase, a table or a platform can all be too small and need to be bigger in relation to the human form. Include paper figures in a small scale maquette and use a drawing of a human form to show the right size for objects on a floor plan. Place your people at entrances, next to furniture and in between crossing paths to see what happens when they need to turn around something or when they need to block one another from being seen by the audience. This is always more accurate than simply using your eye.
The stage directions of the actors can be affected by their sightlines and visibility too. Something safe at the back can end up in the way of an actor in the front of the stage if it stops behind a platform. A tall object placed near the front of the stage might stop an actor being seen deeper in the scene. You can photograph small scale paper models to check from a number of different audience angles. Stand in the middle, stand at one side and stand at the other, to see where the pathways are and where things interrupt the view.
You do not need to make every element of a design smaller if you want to leave space to move through the world. Rather, ask yourself if each element needs to be there and if the position of each object serves the moment. You might simply move one platform round, change the angle of one table, make one door wider or remove one flat to give you more space. A good stage set will allow you to see what is going on, it will not hinder the actors from achieving their task.