When visiting Rome a map is a necessity. Although the city isn't that big there are so many small streets so you can easily get lost or miss what you are looking for! I used the lonely planet map from the guide book.
TIP: When planning a trip to Rome take a map and circle all the things you really want to see. I did this when I first visited Rome as it meant that I look where I was on the map and then see what thing were nearby that I wanted to visit. It also means you don't go to one area and then realise hours later that there was something you really wanted to see one street away!