Italians are renowned for being a warm and welcoming people. You'll find that the majority of Florentines, especially shop keepers and restaurant workers have some English language ability and it is not hard to navigate the city with limited Italian language skills. However, it is best to learn some Italian before you arrive.
When out and about you may notice a few unwritten rules of etiquette that come in handy to any visitor to Italy. Greetings, even when meeting someone for the first time, are warm and friendly. Though smoking is prohibited in all public places, it is still an acceptable habit and it is not considered offensive to non-smokers in the same way that it might be in the United States.
When dining out, "il coperto", or a cover charge, is customarily added to the check. Tipping a specific percentage above the final bill is not the norm, though it is always considered a polite gesture to round the check up and leave a few extra euros after the meal. When ordering food it is important to remember that in Italy you cannot send your food back without getting charged for it. Make sure you know what you are ordering first. It is also important to know that in Italy lunch or dinner is usually composed of several courses.
Something that is important to know about Italy is that despite their reputation for being open and friendly, Italians are a very political people. Italy has had over 60 types of governments since World War II. The political environment is both fragile and steeped in controversy. In a country such as this, the Italian people find staying abreast of their leaders and the decisions they make extremely important. You are likely to learn a lot about current politics once you arrive, though there is nothing lost in doing a little research beforehand.