I will arrive xian midnight & will be staying at city hotel XA. What's the best way to get there?

You can take the airport shuttle bus line 1 to its terminal at the Melody Hotel, close to the Bell Tower. Then pass the Bell Tower to reach the South Street and walk along the South Street to the second T-junction road. Then turn to west side to walk to your hotel.
From the Melody Hotel to your hotel, the distance is around 500m.