Probably the best book I read last year was Never Split the Difference by Chris Voss.
I've never negotiated a salary before but this book gave me the tools and most importantly the courage to negotiate. It says how if you're an honest, hardworking person there is no reason you should feel bad about asking for what you want.
It has all these different techniques on how to frame your arguments, real examples/stories, overall human psychology examinations.
For example, asking for what's fair, use a range when negotiating so it seems like you did calculations, a range seems less aggressive as well (Say you want $65k salary and currently make $60k, you ask for a salary that's fair based on research you've done in the range of $65,219 - $68,778). There is no harm in asking for the $68k and often times people meet in the middle, and if they do you're already above where you wanted. Another tip is don't go first as well. He has a bunch of tips about how to wiggle free from that question because say you ask for $65k but they were going to give you $80k, you just shot yourself in the foot.
Honestly fantastic book and I recommend it to anyone who will listen.