If you want to get your feet wet with a short writeup online, I found these two blog posts (part 1 and 2) to be extremely valuable. It does a fantastic job of making sure you're mentally framing the situation correctly, which makes an enormous difference.

part 1: https://haseebq.com/my-ten-rules-for-negotiating-a-job-offer...

part 2: https://haseebq.com/how-not-to-bomb-your-offer-negotiation/