Getting to Yes : Negotiating Agreement Without Giving In by Roger Fisher and William Ury
[ISBN 0140157352]
Basic concepts (also Chapters 1-5):
Later chapters talk about some additional techniques, most notably BestAlternativeToNegotiatedAgreement.
Read this book now and re-read before you negotiate.
Yes, read the book and practice as much as you can.
I recommend as an alternative StartWithNo by Jim Camp. Getting to Yes used to be my all-time favorite book on negotiations until I read Start With No. Don't let the title scare you off, it's actually a very good book. -- StephanBranczyk
I've written a little on how these principles apply to software development. See http://www.agilekiwi.com/negotiation.htm -- JohnRusk