How to I get taxi in Beijing capital international airport ?

Here are the areas where you can easily catch a taxi at the airport:
T1: Outside Gate 1 to 5 on F1
T2: Outside Gate 5 to 9 on F1
T3: The area is easily to be found by refering to the signs inside the terminal building

Well, if you want a taxi which is running, just flag down to catch that!