First you need to figure out what you want to pay monthly if you are going to finance it. Have trade in? YOU figure out how much you want for it. Don't tell the salesman. I have bought many vehicles in my life. I use this approach when I walk into a dealership ~ find the truck I want, test drive it, go inside with the saleman and tell him or her this: "You only have one chance to get my business and that will depend on my monthly payment, what you will give me for a trade-in and the lowest interest rate possible - remember, you have just ONE chance. If salesman comes out with figures that you feel are way off, simply get up and walk out. Oh they will chase you to the door but just keep on walking, get into your trade-in and drive off. Your phone will ring that day or at least the next.
So basically, don't let them know anything about where you want your payments to be, don't tell them how much you want for your trade-in - don't tell them anything!!
Just make sure they come down on their price for a new vehicle or up the price for your trade-in. I just checked on a 2015 Ford for the heck of it. Sticker price was $67,000. However they were having a sale and marking these trucks down by $7,500. So you know when their sale is over, they have a lot of mark-up money so they can afford to still drop their prices. I refuse to sit there while the salesman and finance manager are talking about the basketball game and at the last minute, scribble down some off the wall numbers for you. I use to sell cars but couldn't stand that back and forth game and believe me, it is a game.