Hm, I used to do that when I worked in a call center. We could do anything on our desk while dialling except anything computerized. So, I would have a notebook and write down either just notes or the whole post, then take it home and type it. I don't usually hand write things unless I have to.
I am a huge list maker. I like to make lists to organize my thoughts. Not always but very often, my post first draft will be a list of lines, character reactions that I put down as I'm going through another read through on my partner's post. Like, usually each item is a line long and is either dialogue or represents a thought I wish to touch upon in my post, usually prompted by something my partner's character said or did in their post. Then, second draft, I put away my partner's post and go through my list and flesh out each item on the list into paragraphs that flow together with a thought process and direction.