There are several options for getting a taxi from the airport to the city center (District 1).
Main taxi queue. The main taxi queue is on your left when you exit through the main door on the ground floor of the terminal building. When you get in the car, ask the driver to turn the meter on. The fare to most hotels in District 1 should be around 150,000 – 170,000 VND and you will have to pay extra 10,000 VND to cover the Airport surcharge.
Mai Linh counter in the terminal building. The Mai Linh taxi company has a counter that is on your right after you clear customs. You can order and pay for a taxi from the staff member there. He will then lead you out of the terminal building to the taxi queue and arrange a Mai Linh taxi for you. As of April 2014, the cost for a single trip from the airport to the city center was 300,000 VND including all tolls.
Other pre-paid taxi counters at the airport. There are also quite a few other counters after clearing customs, though still within the airport building, where they sell prepaid taxi vouchers.
At the domestic terminal, a company called Sasco has the airport taxi concession and is the only company allowed to pick up passengers directly adjacent to the building. Their cars are the first you will see as you exit the terminal.