As I mentioned in another comment, I personally prefer just setting a salary range I’d be willing to accept. I walk away if given an offer below that range. It gives me the initiative of anchoring the negotiation to a number I want.
It also saves me a lot of time by screening out companies that aren’t willing to actually negotiate.
"Yeah thanks, but that offer is not enough for me to leave my current job. I need at least X more. Let me know if you're interested."
(In fact, you can negotiate even AFTER you accept it!)