For my last couple of shows I've started printing double sided with a large margin. Less sheets of paper means less weight, smaller folders, less space on my bookshelf at home (I keep all my folders).
I print at about A5 size in the centre of an A4 page. Nearly all my notes go on the outside margin (opposite the holes), but will use both sides sometimes.
I keep most of my notes short and to the point and write small, with a 0.3mm mechanical pencil, and once things stop changing I re-do all my notes with a 0.3mm Zebra Sarasa black pen (amazing pen!) for improved legibility. I also switch from pencil underlines to highlighters during this process.
Plus I have thin colour coded adhesive tags everywhere. Thousands of them.
I use full notes at first, but for most of the script switch to abbreviations. If someone else calls my show they might see "Robert Enter DSL" above an orange tag, but later on it will be "R. DSL" above the tag. By then they will have learned Orange always means an entrance and there's only one character with an "R" initial.
Sometimes I insert a blank sheet of paper as "page 42.5" for additional notes. So far I've only ever needed that for the beginning of the show and interval.
Finally, I use the binder for storage and transport. During the show or rehearsal I'm working with loose sheets. That way there are no rings and I can jump to other pages without losing my place. If I need to discuss something in detail, I can just grab that page and walk over to another person, instead of trying to carry the entire folder.
Being relatively new (5 shows) I'm still developing my system, but this seems to work well.
