I keep my notes brief but to the point with some acronyms like TAG(tight aggressive), LAG(loose aggressive), CS(calling station), ect.. I will make a note of someone who likes to donk shove and other bad/exploitable traits if I spot them. I have a lot of people I just write idiot if they just play bad. I will make a note of good players also(super important).
I'm just getting back into online poker after a long hiatus after black Friday so my note taking and overall skills are a bit rusty. I never was a fan of HUDs either but if I suspect someone is using one I will make a note.
Unfortunately I am restricted to playing on my cellphone because I am going through a messy divorce and the ex wife took the computer and most my money