If your Ferrari or Porsche is in the garage, or you haven't hired one for your stay in Monaco, the best way to get around is using the bus network!
There are six lines which will take you pretty much anywhere you need to go within the Principality. It's worth bearing in mind that Monaco is very hilly and supported by a system of public lifts which take the strain out of any ascent and might mean a shorter journey than taking the bus.