Everyone's a comedian so here's some actual advice.
TLDR: be polite but firm, know what you're asking for.
Lots of activism and lobbyist groups have the concept of an "ask", or what you're attempting to get out of the negotiation. Have a solid, easily understandable ask that is generous enough to withstand a bit of pushback from the other party, who will almost certainly try to negotiate the other direction. Also, when you deliver a statement, question, or ultimatum, wait for the other person to respond to it, even if there's a couple seconds of silence in between. Conventional wisdom says the one who speaks first in these moments is displaying insecurity and is less sure of their ask or position in the negotiation.
Good advice. It's also good to have clear boundaries set up. The ideal. The what you expect, and the non negotiable. Start with the ideal. Expecting to get pushed towards what you expect. Never budge on the nonnegotiable.
Silence is a weapon. People don't like awkward pauses and will talk to fill in the gap and sometimes they end up putting their foot in their mouth.
I use this all the time. At some point in my life I just stopped being uncomfortable with silence, but it drives most people mad.
And it's not just useful in terms of having an "opponent" stew in some social discomfort.
Use it to take a moment to think. Use it to give the other party time to think. Use it to let your most recent words hang in the air and gain more weight. Etc.
I did contract negotiations for a while. Something that I always remember being told was "you can't be more excited to sign than the other person". It'll lead to you making bad deals. If the other side doesn't want to sign, neither do you.
My boss always said he preferred no contract over a bad contract. I once suggested that even a contract that pays out a bit is better than nothing. He countered by saying there's an opportunity cost in fulfilling a contract. We could be too busy fulfilling poor contracts that we have no time to negotiate and accept good ones. In that case, a poor contract could be seen as less valuable than nothing. I've had negotiations that lasted less than 15 minutes. I give a standard quote, they'd lowball, I'd say there's no way, they said they'd leave, I say here's the door. Done.
I work in procurement. That means I negotiate with suppliers all day, every day. I'm the one the team calls when they need something fixed, and want something better than using a big hammer or lighting everything on fire.
The absolute best tip was courtesy of my first boss in the field:
"Always be prepared to walk away and say 'No, thank you'. "
You won't look weak (except to the wrong people). Instead you'll come across as empowered, that you know what you want, have no tolerance for games, but also can be trusted. Very few people like people who always say yes, no matter what anxiety says. In order to be here, it's important to have options and choices you can accept. Be ready to jump rails if it looks like you won't get your first choice. That's how good negotiators in my field do it - they have several acceptable options.
It's still not easy to do. It requires perseverance and flexibility. Allow yourself to practice in lower-risk situations.
Read some books on the subject
Never Split the Difference might be appropriate. Influence: The Psychology of Persuasion is a great read. Getting to Yes/Getting Past No may also be decent.
Understand "what kind of cards you're sitting on". Before that even happens, ensure that you have good cards
Concrete example: You're looking to increase your salary. You can do it either by convincing your current workplace to increase it, or you can look for a new job.
The cards you're sitting on: How valuable you are to the company, and how likely you are to leave if you don't get what you want.
How to improve your hand before you get to the negotiating table: Try getting some competing offers for jobs.
If you're the less experienced negotiator, avoid negotiating live
When negotiating salary for a new position, the recruiter likely has far more experience negotiating. They will know techniques to try to get you to commit to a lower number than is possible. To avoid this from happening, move negotiations from in-person/on the phone to email. Give yourself a lot of time to process all information.
Tinkering with technology is my hobby, so I spend a lot of time on secondary markets (like Facebook Marketplace, OfferUp, Craigslist, eBay, etc.) I always research the original price of any item I'm interested in, any current discounts being offered by retailers (like Amazon, etc.), and what the average pre-owned price appears to be across platforms. Then I offer some amount less, and expect a counter. I equate negotiating with fishing. I know that, with patience, I will eventually find a motivated seller. So I try to never enter any specific negotiation needing to make a deal. Obviously the rarity of an item and your desire to obtain it are big factors that will influence the price which you are willing to pay, but knowing the item's value and being unafraid to make a reasonable-but-low first offer has proven successful for me. Also be courteous. I have had better success providing context and asking questions about the item then merely opening with a low effort bid, and have even had several sellers return to the negotiation hours, days, or weeks later because I invite them to if we are unable to reach an initial agreement.
This is an article I always reference for job offer negotiations, but the principles would apply to negotiation in general. The most important concept to understand is: you can split a pot between two parties in ways that result in both of you getting more of what you want.
Yeah, but I would say it's less important that you can find a win-win solution, and more important to get in the mindset that advocating for your own interests is not the same as being selfish.
A lot of people fail at negotiating because they don't want to be seen as selfish, but especially when it comes to negotiating with a corporation, they're banking off of you feeling that way. Know your worth, and make sure you're fairly compensated.
On a related note, this is also the point of a union/collective bargaining and why companies hate them. They know that some people are better advocates for themselves than others, but they know that most people are bad at it. Divide and conquer.
Read books about how to negotiate. You can stand on the backs of giants. I'd start with "How to win friends and influence people" by Dale Carnegie, as it's a good guide on how to just deal with people.
This gal has a channel devoted to things like this, particularly in regards to career-related settings. Lots of good advice here:
There's no way I can do that. I'm much too busy shitposting. It would be a huge inconvenience.
From The One Sentence Persuasion Course by Blair Warren: "People will do anything for those who encourage their dreams, justify their failures, allay their fears, confirm their suspicions, and help them throw rocks at their enemies"
I've found this helpful when trying to convince anyone of anything. The book breaks it down more, of course, but is probably not worth reading Vs the various summaries you can find online.
My summary, at least what I took from it is that you must try to understand the person you are negotiating with/pursuading. Figure out what they want, or what they're afraid of, and offer that.