easiest way to make (usefull) notes are two steps:
- learn the abc sng style (like 3betting QQ preflop

)
- make notes on the way people differ from the abc strategy.
Notes are most important on regulars (or really every player you see alot).
You can't really apply the notes from the above posters, since postflop and preflop situations in sng's are far less complex.
I use this note system (assuming 10/9 max sng)
22$ sss m 5% BSS
- buy-in level
- s: spotted. It's a system to use your 5 sharkscope searches on a efficient way: every time you see someone you think you saw before: tag him with s. If you see someone with an s, add another. When a player has "sss" --> sharkscope him. If he's a regular you can change SSS with R (for regular)
- m: multitabler
-X%: ROI% found on sharkscope
-BSS: big sample size-- as Oposed to SSS
So that one line tells you alot about the player allready. Next I try to make notes on the way villain plays there hands, and I only write down the things I dont do.
examples:
- 20 3bet JJ IP FS
blind level 20 -- villain 3bets JJ preflop- In position- Full stack
Make notes on the key hands: 3bet with JJ AQ AK. This will tell you alot about the preflop range, which is super important vs. regulars
I rarely make notes on postflop play (unless they are real solid) because postflop is pretty easy: Go broke when you hit - potcontrol/fold when you dont.
For the lategame (high blinds) I make notes like:
- pushes loose from button
- calls loose (good) from BB ------------(most players call too tight)
- loose from SB
-....
So my notebox can look like:
22$ R 7% 33$ ss 3% SSS
20 cc KQ IP
20 3bet AKs OOP FS
40 minraise QQ UTG HS
Loose from SB
-$EV pushed UTG (good)