Make sure you have credit lined up before you visit any car dealer. The low interest rates offered by car dealers means they have to make up the loss by charging you more for the car.
Go to car dealerships outside of main metro areas where the rent and cost of living is much lower; you'll get a much better deal.
As you probably already know, the sticker price doesn't mean much, because of the markups embedded in that price. The other is that dealers gets factory discounts that do not appear even on their "invoice."
Depending on the make and model, try for the biggest discount you think you can get away with - like 25% off the sticker price. Tell them you'll pay cash.
If they let you walk out of the salesroom, you know that's too low. Play that game with several dealers on the same car; that'll give you a feel for what the bottom price is. Negotiate tough; they want to sell, you have other dealers for competition.
Most car salesmen will say they need to get the approval of their manager; a tactic that doesn't mean anything - just a delay tactic. You will go back and forth with the price, because they want to make it look like they're negotiating in good faith, but they are not. They already know what the lowest price is for that make and model.
Ask them; what's your best price. Tell them you'll go see another dealer if they won't offer you their best price. Then offer them several hundred less.
BTW, there are magazines that lists factory price and retail price by make and model. That might be a good place to start.