Talking a dealer down on a 04 G35 coupe?

Alright this is the situation. I currently have a 03 Mits.Galant that I know im not going to get **** for but okay. I owe about 8,000 on it now if i trade it in i think that im going to get like 4500 for it around there and then the remaining money will go ontop of another car that im looking at which is a 2004 infiniti g35 coupe its got 46,472 miles on it. Im 20 years old a girl if i go into the dealer how much do you think i can get them to lower the price oh by the way the price of the car is 18.995, now i need some tips on how to talk to them and get them to lower the price i know people say not to pay the orig, price get them to lower the price i need some help ! serious answers only please thanks !!