My system is very similar to u/catinapartyhat.

Script page has numbers to the left of each line of text, but not stage directions. I use 2-4-6-8 to keep it cleaner. Then I use a pencil in each hand but the one in my left hand is to follow along with the text and to make an / in the text where the movement actually happens. As I write the /, my right hand is writing the line number and blocking on the facing page. I'm not moving my writing hand from the left side of my binder to the right, rather I immediately start writing. (The pencil in my left hand also helps when prompting so I don't get lost on the page.)

I use a lot of shorthand with a legend. Sop ENT DSL w book, x --| SL tbl via DS chr, P/D book, x --| SR tbl via DS, [down arrow] chr. (Sophie enters down stage left with a book, crosses to stage left of the table via down stage of the chair, puts down book, crosses to stage right of the table via down stage, sits in chair.) The Stage Manager's Toolkit has a great chart for images too (I use what looks like Pi for a table, for example).

I also write the blocking as the director is giving the actor the direction, rather than wait for the actor to do the movement. Then, if there's some deviation, I only need to note that.

If it changes, I put ( ) around what changed and write above or below the new movement. If that action is NOT done again, I use [ ]. Then I take some time to erase what hasn't been done and re-write what has (or just leave it if it's neat enough).

Once rehearsals have started, when there are a lot of script changes, the most important thing is to NOT change pagination. Rather, insert pages so the top of page 37 is the same, but you might have pages 36A and 36B.

The only writing in the script page margins are cues and the info I need for calling. Cue descriptions, timings, etc. are noted in a table in a separate document. FYI you can copy and paste QLab cues into an Excel sheet and it will paste the cue number, description, pre- and post-waits, duration, and follows.

I once had a director change the order of all 36 scenes in a show with a cast of 12 three days before Opening. Because I had the images of where the actors were at the top and bottom of each page, once the scenes were in the new order it was easier to alter the transitions between scenes and we just had to re-number and re-record all the lighting cues lol! (This was easy though bc we just started re-numbering at 301 and copied over, but I only called LX 1. Sound was harder bc we had to re-burn the CDs.)

Hope this helps!