Sell your car to the dealership you're buying the new one from, and you'll save in taxes.
It wouldn't hurt to get your ride appraised at Carmax for a little bargaining power.
Go to whatever dealership has the vehicle you want to buy. Take a look at the first pencil, but don't even worry about your trade during this time. Do your research beforehand on what you should be paying for the vehicle you're trying to buy, before you negotiate anything else. It was always easy for me to move numbers around the four-square, when people only really worried about trade-in values. Once you get the bottom dollar on the vehicle you're trying to buy, then it's time to talk about trade. If they hit you at $10k and Carmax is at $12.5K, tell them you want $15K for your ride. Your goal is to try and get them to beat, and at the very least, match the Carmax offer. **Do not show them or tell them about the offer until you've tried everything and they're not at the offer.** Oh, and don't get caught up in the Bluebook value, because it doesn't mean ****. I used to tell people to call KBB, their bank or whoever gave them that crazy price, and see if they wanted to buy their vehicle.