Given my technical background (SWE), I have found only one useful tip for salary negotiations during a job offer: get atleast two offers and play the companies against each other. I've found nothing else to be effective.
Basically: have a real card to play that they think you might play. Companies will empathise to the end of the earth with you about anything, however you have to have that card.
That might work if you have a unique skill that both companies need, but if there's another appropriate candidate to hire instead most companies will hire that guy and recommend that you accept the other company's role.
What my company offers is based what value you're bring to the business. If another company sees you as more valuable that's brilliant, but it doesn't change what you bring to mine.