My favorite resource for clients who are new to negotiating is still this 2013 video by Margaret Neale, of Stanford Graduate School of Business. You can save a little bit of time by watching it at 1.5 speed, but I think the whole thing is good.
I’ve created a worksheet based on Neale’s suggested preparation strategy to help clients prepare for workplace negotiations; if you think it would be helpful email me with the subject line “Negotiation” and I’ll send you a copy.