Have a set price before going into the negotiation that you will not pay more than. Also have a price which you would like to bring the dealer down to, NEVER EVER EVER TELL THEM WHAT YOU ARE WILLING TO PAY!! The good deal is all what YOU feel is the good deal, if you come out satisfied with the negotiation and feel that your needs were met. Keep in mind if you cannot negotiate a price you can always try to squeeze in extras many people don't think about, service dates they could do, pay for tax/tag/title, you just have to think outside the box and figure out what you want in the end. If it is the lowest price, like I said go in their with a price you want to pay and the highest you will settle, only settle if you feel needs are met, like if the dealer will not budge on the initial price, ask to throw in something else, like an upgrade to the stereo or something(just an example). Bring print outs of NADA and KBB with you, be prepared for their, "well we need to make money too" lines and such. In this type of negotiation you are not trying to care what he gets, you want what is best for you. Just research and be prepared. Be confident in everything you say, it will go a long way, don't let them push you around with numbers/financing and other jargon.
Good luck!
__________________
