If it's a new car a good rule I've gone by is negotiating the final price of the car (after taxes, fees, etc.) right near what the dealer is asking for as the msrp. You only have to do this if you don't have access to invoice prices. If you have the invoice price then it's that + 500-1k for dealer + taxes/fees.
If you are a USAA member buy the car through them. They negotiate a very good price for you, and you just walk in to sign the papers because deal was made before you walked in the door!
When/if you trade in your old car, don't use it as part of the deal. Make the car purchase a separate deal. After a price is finalized and agreed upon, then attempt to sell them your used car. let's say your car is worth 2500. The dealers will inflate the sticker price of the car you're interested in and then tell you they're giving you a 5k trade in value when all they are doing is taking your car for nothing.
If they don't want to buy your car after you make the deal on the new/used car you purchase then sell it privately afterwards.
Also don't get anxious at the dealer or fall in love with a car. You can walk away from any deal. There's enough inventory out there that another car that you like will show up in the area. Walking away from a car deal is harder if you're younger so good luck if you're under 25 trying to do this on your own.
Finally don't get a Dodge....just don't.