Put as much down as you can.
Look the numbers over carefully. Some dealers will try to get you to look at the total all in price while others will focus on your monthly payment. You should know both. There is always room to negotiate your rate. Most big dealers have good rates but it doesnt hurt to check with your bank to see if they can offer you something better. Then you can leverage that at the dealership. Get them to throw in something for free. Better mats, roof rack, tints. Get something from them.