The power of words is crucial when writing for theatre but so is a technical understanding of the staging process. Writers need to do the following:
Think where the person was before entering the stage and where he/she goes to eg if he/she has come in from the cold remember to write cold references of actions (stamping feet etc )
The writer needs to consider what the characters are doing as well as saying - a walk across a stage can take a long time as can a passage of speech. Find something for them do, making tea, putting the kettle on etc. It gives the scene more movement and avoids problems for actors who feel all they can do is stand like a plank and spout their lines.
Think of how long words take to say and how they will play in an audience. An intimate aside in a small room can fall flat in a large theatre.
Comedy needs to big and bold, drama can be more subtle and considered (the actor can be more introspective, address the audience, reveal much about what they are thinking)