Best way to visit Florence is a walking tour of the city. Everything is interesting, from historic buildings, art, museums, churches; or just walking down the street seeing the massive homes with multi-story gardens. Restaurants are fabulous, the people are kind, and there is so much you want to take home with you!
What I loved most about the historic center of Florence was the beauty of so many of the old buildings and also the fact that much of the old part of the city was cobbled and free of vehicles. Not having to doge cars made this part of the city very nice to stroll around.