Will arrive at Xianyang Airport at 11.30 pm and plan to take a taxi to hotel

In T2, after leaving the baggage claim area, walk to Exit 2 and make your way across to the cab stands.
In T3, after leaving the baggage claim area, find Exit 314 and make your way to the Ground Transportation Center (GTC). Then cut across the hall and leave the building through Exits G08 or G09 to arrive at the cab stands.
Generally speaking, you can easily find the right way according to the clear English signs at the airport. As I know, the official cabs are yellow and green colored on the body.