Metro Line 6 red has a stop La Villa-BasÃlica about 2 or 3 blocks from the basilica complex. Line 6, a fairly isolated line which runs east-west to the north of the city, has several connections "correspondencias" to lines that service the rest of the city: Line 7 orange at El Rosario, Line 5 yellow at Instituto del Petróleo, Line 3 green at Deportivo 18 de Marzo, and Line 4 teal/aqua at MartÃn Carrera. From any of these stations, hop on Line 6 to La Villa-BasÃlica. Exit the station, follow the crowd through the narrow market-like sidewalk full of food stalls, and onto the Calzada de Guadalupe the main thoroughfare. From here, the Old Basilica should be visible; simply follow the crowd the couple blocks to the gates of the basilica complex. The New Basilica will be on your left, and straight ahead, the Old Basilica and the Capilla de las Capuchinas.
You can also take a taxi from anywhere in the city if you'd rather deal with Mexico City's eternal traffic than the Metro.
