For most people, the purchase of a new car is a dazzling and powerful emotional experience. Unfortunately, this emotional state makes them ripe for manipulation and easy exploitation. Additionally, most people negotiate monthly payments attempting to keep the payment as low as possible. At least they should be. Others, negotiate out the door price.
I prefer having my financing in order prior to arriving at the dealership and negotiate an "out the door price", attempting to keep the final sale price as low as possible to minimize annual registration fees.
I usually start at 20% off sticker. When they run my credit check and fund verification they are eager to negotiate. On one occasion they said what can we do to make the deal and I said sell me the car 15% off sticker and they did. Now I think I would reassess and start at 25 % off.
Anyways, I wouldn't be in a hurry and expect multiple trips to a dealer, if for not any other reason than to par take in some of their instant coffee and stale crumpets in a lobby filled with the local hoity-toitys.