The most convenient way to reach the Temple of Heaven is by the Beijing Subway. You should take Line 5 and get off at the Tiantandongmen Station. From there, use Exit A, and the East Gate of the Temple of Heaven complex is just a short walk away.
Several city bus lines serve the Temple of Heaven, including routes 6, 34, 35, 36, 39, 41, 43, 60, 116, 525, 610, 684, 685, 686, 707, 723, 729, 732, 742, 743, 744, 753, 958, 957 and Special Line 11. You will need to check the bus routes for the closest stop to the gate you wish to enter.
Taxis in Beijing are convenient and can take you directly to any of the four gates of the Temple of Heaven Park. Simply tell the driver "Tiantan Gongyuan" along with the specific gate you want to visit (East, West, South, or North).
If you are driving, there are parking lots available near the East, South, and West Gates. However, please be aware that traffic in Beijing can be heavy and parking may be limited.