You're required to come out of the terminal gate and then follow the sign to the taxi stand which is the correct and only good place to take a taxi.

Illegal taxi: just like street vendors, those guys keep bothering the passengers at the exit, especially the foreigners. Generally, they would say "Hi Sir/Madam wants a taxi?" If passenger shows any interest or even hesitates, they would follow & persuade him/her for long. You'd better ignore them. Some of them even dress formally & have a license (not real) to pretend to be legal. So, be careful when you try to take a taxi. Otherwise, you will pay a lot from these illegal taxis!