And geez there's a boatload of things to take into account and they have to become second nature (like playing a sport or self defense) so you just have to spend time and practice all the time and keep practicing.

I actually keep my own notes on all my thoughts and techniques that pop into my mind.

Here is one as example.

Timing. Timing is important. I take into account not only how quickly someone replies but how quickly I reply or get back to someone. There is a reason and a strategy behind what people do in most, but of course not all cases. Even the time of day they reply and the length of the reply and exactly the words they use as well. Say when you propose something how quickly do they get back to you? All context in different cases means different things.

Also timing as far as when you spring things upon people.

For example I'm currently in the process of getting my bathroom quoted for remodeling. I've settled on a particular vendor that I'm pretty sure I will use. We've been going back and forth on details for probably 6 to 8 weeks. They've given me pricing and I haven't asked or said anything regarding getting a discount. At all. I also haven't asked for any exact details on products they are using. I don't care at this point.

What I will do is most likely bring up a discount at the very end of the process. When they have already spent time on the deal and don't want to lose it. [1] I will also bring up other factors to them (non monetary but convenience for us) at the end. I know they won't be as likely to blow off those concerns after the big investment in time they have made.

[1] After listening to my war stories my ex wife used the same technique against me when we were ready to sign our divorce papers. At the very end as we sat there the deal all done and papers ready to sign she said "I'll only sign if you also pay for my trip to XYZ". While I could have walked she knew me well enough to know that I wouldn't and actually I was kind of proud that she had listened and learned. Which is another point in order to negotiate you have to know as much as you can about the motivations of the other side as possible. (So research is important).