taxi cost from Bangkok Airport to city center?

Tomorrow morning Im arriving in Bangkok. Since nobody will wait come to pick me up, Ill have to take a cab from the airport to the city center. I know that it can be very expensive so I wonder how much it can cost. Is there anything else I should pay attention when in a cab? Do they use a taximeter or charge approximately? Thanks in advance.

Well, I know the cost is about 300 baht, and the best way is to use the meter. When I went to Bangkok for the first time, a cab driver ripped me off, because he told me it would be cheaper without the meter, and we agreed on 500 baht, which is as you can see almost twice as much as the usual cost. And, you should know that youre supposed to pay all the tolls along the way. So, just insist on using the meter and enjoy the ride.