Here is a link to some of my favorite spots, if you are starting your day arriving at the train station.

The historic center of Florence is easily covered from end to end in a half hour of walking.  Additionally, very few of the streets in the city center are setup for any sort of meaningful movement of automobiles.  Traffic moves slowly, and there is simply no where to park.

If you want an adventure, rent a moped for the day and cruise around the perimeter of the city or up to Fiesole.  Bikes are also a unique option, and can be rented easily.