I have always kept two books, a "directing" book and a calling book with minimal blocking, only as it applies to cues.... as such, it has always seemed best to put the pages on the right and use the left for quick notes, etc. When taking blocking, I usually have one quickly annotated book, sometimes messy and besmudged with eraseures and then a "neat" book after opening with stage direction on the left side, stage diagrams for large crown or chorus numbers, etc.
Here at the Opera, we use the same books over and over, so the format and style must be the same so that any SM in any season can pick up the book and run the desk or deck SL and SR. Our "rep" shows often only have one stage rehearsal before opening, so accuracy and clarity and non-personalization is very important... no one should have to ever figure out what the various symbols, etc mean, or whole measures and pages can go by in a trice!!!!