For work, with a nice A4 pad:

I only date if it's a meeting/phone call. Otherwise I'm a bit lax, never found that to be a problem.

I don't distinguish between scratch and "tidy". Tidy means it probably should be in a version controlled document. Which means I usually draw a box around it to remind myself to document it.

Also I place a single diagonal line through "dead" pages or parts of pages. A good reminder to go back and document/deal with stuff that isn't crossed out.

I've played with folding/snipping corners of dead pages, leaving only very useful stuff un-folded. Works well for day book type stuff, but not if you're noting concepts/ideas you'll reference again.

I leave the first pages free, and have some kind of index/overview.

Back pages are usually for quick notes that are unrelated to current stuff.

If it's a new project, always flick 2 pages or so forwards, to give space for tidy up of old project/handover work.

For less formal notes, I use coloured stickies in my notebook - good for phone numbers/email addresses of people in meetings/on calls/to contact.

Whilst one-note looks great, my notebooks consist mostly of: diagrams, free form tables, nested lists & flowcharts. Only if I'm reviewing for personal use do I have dense text.

Want to figure out how to integrate whiteboard photos into my processes nicely though!