While working with the scriptwriting everything was mapped out with mathematical precision, even where the actors should look, camera angles and how the scenes should be used in the cutting room.
He didn't write the scripts himself, he had a panel of writers working for him. These writers met him and Alma (who had "final cut") every day, which gave him the opportunity to tell them exactly what he wanted.
When he made a script it was already to begin with divided into "shots" containing a description of camera angles, composition, lighting, setting and duration - he made a detailed description of the visual sequence. When this was done he had the writers write down the dialogue. The reason why he worked like that was that he wanted to tell a story using only purely cinematic means - when the sound film was introduced it became possible to make "pictures of people talking" (i.e., it was possible to make a movie containing nothing but dialogue without having to master any cinematic skills).
The script was so detailed that the movie was almost cut before it was shot.
Hitchcock found it difficult to work with authors who had already made a name for themselves, since he didn't really need an independent writer but a skillfull secretary that knew how to write down his thoughts, in a way that filled in the holes in the movie's "architecture" in a reliable way.
In addition he had a tendency to differ from the literary source when the movie was based on a novel. He only used the central plot, when the book was read he forgot about it and made a movie of his own, containing other characters and scenes and a completely different story - he didn't make what you would normally call a screen version of a novel.
In the script everything was mapped out in a degree that gave him total control of the movie's creation. The only aspect of the movie he didn't control during the scriptwriting, was the music. But he had a way of exercising complete control of the music too. One of the composers from the British era, Louis Levy, have told that even though Hitch knew nothing about notes, arranging and orchestrating, you would still leave the meetings with a melody inside your head - he knew exactly what he wanted and how to formulate his requirements in a clear way, that left the composer without any doubt about how to write the music.
Hitch's idea of an ideal film was a movie were the dialogue didn't support the visual sequence, the dialogue should contradict the visual sequence. E.g., if a woman is crying she don't have to say she is sad - that is obvious, the line would be needless (the line could contradict the visual sequence by saying something like this: "Oh, don't make me laugh!"). But to his regret he had to recognize it would demand too much time having the writers write the lines, if the dialogue should contradict the sequence through the entire movie.
Production Code and their claim for a happy ending forced Hitch to adapt and turn the rules into his own advantage. This resulted in his speciality: the ambivalent ending, i.e. an ending that seems happy if you look at it in a superficial way, but if you give it a more thorough consideration you know it isn't what it seems to be. He also used this ambivalence for characters, i.e. a character that isn't what he/she seems to be - this can be used to make the hero look weak and unsympathetic, or make the villain look sympathetic. This ambivalence was - in combination with the use of suspense and in particular active camera - used to make identifications. He could among other things make us identify with the villain - as he said: "The better the villain, the better the picture!".
In addition he preferred to use cinematic virtuosity in his work. He would often film the scenes in an unconventionel way showing virtuosity, which gave evidence to eminent skills.