The best restaurants serve simple food with very fresh ingredients grown in the nearby countryside and no rich sauces. The most important ingredient is a pungent green extra-virgin olive oil, cold pressed from the Tuscany olive groves. This is used as a dip for celery, artichokes, and other fresh vegetables, as well as a salad condiment and topping for bruschetta.
In the historical centre of Florence you will find plenty of fine restaurants offering typical Tuscan cuisine. Ask your hotel to point out the best Tuscan restaurants in Florence.
You should also definitely try out the enoteche. Once serving only wine, today they are light-meal restaurants in themselves, serving panino or bruschette alongside their excellent local wines. Once on a par with cafes, enoteche are now respectable eating establishments in themselves, adding world-class light foods to their already extensive wine lists as attractions.
You may not think of Florence as a huge ethnic enclave, but as a world-class city, it holds a wide variety of peoples. If you're tired of Italian-style cuisine (far-fetched but possible), Florence holds world-wide restaurants, most commonly Chinese, but also Indian, Japanese, Jewish, Mexican, and Caribbean. There are several vegetarian restaurants as well serving international cuisine, but if you're a vegetarian you should not have any trouble finding good meatless fare in most ristorantes and enoteche.