If so, what do you write down?

I started to in the beginning but at SERRA's there are just too many moves that you’re better off just rep’n over and over and it becomes muscle memory. The instructors do a really good job of rep’n the moves in class and drilling them into your head because they might not teach the same move for another few weeks. In the advance class, every day there’s something new, you can go months without Matt/Danny/Mike/Nick teaching you the same thing twice. I use to write things down like the different sweeps from half guard, full guard, mount... etc.

yea i tryed to but i couldnt keep track of all of thee moves =p

I keep a binder, but i try not to write EVERYTHING down. It just becomes too much. So what I do is divide the binder up into sections. Guard, Half guard, mount, etc. Then, i just keep little mental notes as the instructor goes over the move. Then i just jot down those notes in bullet form in the binder. I find it does have some usefulness.

I have a small book.

I start off with the date, followed by the instructor who taught it (should I have questions later). I like pictures so I draw a little doodle pointing things out. I've seen others write out everything step by step.

One thing I write down is weight positioning because I've always had a problem with that ("put foot/leg/arm/chin here" or "keep torso here").

I fully agree with Papolito20's "rep rep and keep repping" statement. The book will come in handy if you have to take time off.

I should start writing in it again; I've slacked off.