If you have carmax nearby, they will usually offer a very fair price on the spot that is good for a few days. The printout is good leverage at the dealer.
You should generally get the sale price locked in before you even talk about trade in. Get them to commit and then treat the trade in as a separate negotiation. Same with financing and warranty - if you have financing lined up before you go in, you'll have some options. A lot of banks offer their own warranty too. Good luck!