As well as my online blog, I ‘blog’ in the old fashioned way, ie I keep a handwritten notebook / sketchbook. I don’t use it for every painting, but if there is a particular color or value or combination I’ve been struggling with, or something in particular I want to solve, I make little notes about it as I go. I take a picture of the painting I’m working on; printout a thumbnail version of it and glue it in my notebook and write notes directly on top or at the side. It might seem long-winded but it’s helped me learn and remember. More often than not I don’t ever go back to the notes, because the process of recording in a written form has lodged what I’ve learned firmly in my head, however it’s there if I need it for future reference.
I think there are a few people who use their online blog in a similar way (Karen Margulis comes to mind. She is meticulous about recording every step of her process).
In general, I prefer to use my blog to talk about the finished work and my handwritten notebook to record the nitty-gritty stuff.
Also I always use a paper palette. I keep a fine sharpie handy and sometimes write on the palette the colors I’m using and take a quick photo which I can reference another time.