I heard that if i take a taxi at Hong Kong, the taxi driver will cheat us by taking a long drive.

Generally speaking, the taxis operated by the big companies are reliable. You are suggested to take the one in red, green or blue color.
Don’t worry, you can estimate the fare according to the distance. If their price is reasonable, you can take it. Or you can make it a deal with the driver before you take the taxi.

By the way, the MTR system is quite convenient. You can also travel with that if you don't want to get cheated.