A common problem in Naples is language. Most people here don’t speak much English. Sometimes, Neapolitan dialect is spoken, so even if you know Italian, you won’t understand much. I recommend bringing a phrase book with menu description, OR when all else fails, just look around and indicate what you would like. That way, there are no surprises and it’s fun.
One note about the bill. As in the rest of Italy, there is a cover charge (called “coperto) of about 5,000 Lire per person. This covers bread and table settings. If there is no service charge added (note this is different from cover charge), then you should leave a tip anywhere from 2,000 to 3,000 for a small restaurant up to 10% maximum for the fanciest restaurant. Usually, a couple thousand lire would suffice. It is very rare to give even 10% tip.