You don't really say if you are buying new or used, because my advice only counts if you are buying new.
1) Don't buy tomorrow (today) if you don't know what you want. You can go in today and look at a bunch of cars, but don't decide today. Do your research and then pick one. If you go in there with the mind set of buying something, but you're not sure what it is, there is a chance they will convince you to buy something you don't actually want, and you'll regret it later. Drive everything you want. Take notes. Go home, Google each car and make a decision.
2) Once you know what you want, go here and buy a report:
http://www.carcostcanada.com/1/en/
The report tells you how much the dealership paid for the car.
Go into the dealer, tell them you know how much wholesale price is on the car and you will add 3-5% on top of wholesale and that is the price you will pay.
I did this with Subaru. I paid wholesale +4% total in May. It's far for everyone. No one gets ripped off.
You could also go to a car forum of the car you are going to buy and ask if anyone has a car cost report that they would be willing to send you. Works just the same.
Good luck.