Remember, Rome wasn’t built in a day and no one expects you to see it one either. At the center of a huge city, the historic districts of Rome are quite large. Streets can be quaint and adorable but there are zillions of them, so pace yourself accordingly; as much as visitors feel they can proudly stride across the city in one glorious day, this would leave them in bad need of a week's rest. Happily, if all roads no longer lead to Rome, many streets in the city lead to the Termini, or Stazione Centrale, Rome's main train station and the city's main transportation hub.
Make sure the bus you're waiting for actually runs during that part of the day or on that particular day of the week. For example, notturno buses (late-night buses), which can be distinguished by the "N" sign just above the bus number, don't run until after midnight and only a few times per hour. Oftentimes, tourists get confused while waiting at the bus stop, since the notturno bus schedules are listed side by side with the regular day bus schedules.
Also, be aware that deviata buses run on bus lines that have been rerouted due to road construction or public demonstrations. And festivi buses are ones that only run on Sunday and holidays. Both notturno buses and festivi buses don't run as often as other buses do on weekdays and Saturdays.
Regular buses will either say feriali, which means "daily," or won't have any special distinction.
The Metro A line will take you to a chunk of the main attractions in Rome: Piazza di Spagna, Piazza del Popolo, St. Peter's Square, and the Vatican Museums. The B line will take you to the Colosseum, Circus Maximus, and also lead you to the heart of Testaccio, Rome's nightlife district.