From Fiumicino "Leonardo da Vinci Airport":

Take the Leonardo Express train (every 30 minutes) to Raiyway Station Termini (duration trip 30 minutes ticket cost 14€).

From Termini station take the Subway Line A (ticket 1,5€)  and stop at Piazzale Flaminio/Piazza del Popolo (4 stops).

Go through Piazza del Popolo, keep right in via dell'Oca go on and you'll be in Via della Penna (200 meters)