We have just spent 3 days in Rome and thought we'd pass on some tips that we would have appreciated before we went there. We found the Roma Pass great value - 3 days unlimited travel on buses, trams and metro plus free entry to 2 attractions and 10 % off thereafter. Metro is quickest way to get anywhere but has limited coverage. The trams are crowded but go by often. The buses are slow because of the traffic. Don't believe all the signs you read, the instructions are often not in anything but Italian and even then the native Italians can be confused by them. For instance when we visited the Vatican museums ( awesome) you have to hand over your passport to get an audio guide. Ok but we weren't told clearly other than ' when you leave' how to get our passport back. Ended up having to walk a LONG way after the visit to do so. When you get caught in a large moving crowd it is impossible to see any signs which may or may not be present. This applies to the whole of Italy - sometimes the instructions are really good and other times non- existent. Be prepared to go around in circles a fair bit and allow time for this especially at train and bus stations.
We have found the do it yourself ticket machines at the train stations to be excellent and save a lot of of time. Also don't forget to validate train tickets in the machines at the platform - we have seen travellers getting fined for not doing so. The train staff don't always check tickets but if they do and yours is not correct they are not lenient.