I've always hated the simplistic "Just negotiate, bro!" advice. I wish it came with more concrete tactics to use that work. I've never in my 20+ year career asked for more money from an employer and got it--no matter how many documents and facts I came in with.

Here's how it goes with existing companies:

[Me] Hi, I'd like a raise.

[Co] Nope.

[Me] OK, here are examples of the value I'm providing and how it's increased over time.

[Co] Your current salary accounts for this.

[Me] Other companies offer 20% more and I'm only asking for 10%.

[Co] ...

[Me] OK, I have an offer from the other company. Last chance.

[Co] Well... Bye?

Here's how it goes as a new hire:

[Co] Here is your offer letter with your salary, bonus, and equity. (it's 0.2% more than my current TC)

[Me] <gulp> I think the market rate should be much higher, based on my experience and skills.

[Co] We don't agree.

[Me] Can you be flexible with the equity?

[Co] No.

[Me] Can you offer a signing bonus?

[Co] No.

[Me] Can you be flexible with the base pay?

[Co] LOL No.

[Me] What about hours, time off flexibility, and so on...

[Co] Look, do you want the job or not? There's a line forming behind you, my dude.

I hate that a skill (negotiation) that is unrelated to my actual job has to be one of the primary drivers of my compensation.