Although relatively expensive, taking a taxi is not a bad idea when moving around in a confusing city or when you are in a rush. The taxi driver can do the navigating for you and they will take you exactly where you want to go. Just say the name of the street or place and you will usually be taken there without a problem.
However, because taxis are usually expensive, try to look for other means of getting around if possible. When you arrive at the airport, politely refuse the herds of taxi drivers as they try to usher you into their cabs. They may try to convince you that they are the only transportation system to and from the airport. Look around for yourself and you're bound to find a train or bus going your way. Many of the big cities next to international airports have either shuttle services or subway / transit trains that will take you to the center of the city. Be cautious of locals 'selling you' on the importance of taking a cab, as they are probably receiving a small fee for referring you to the cabbies.
In third-world countries you can usually hail a taxi from anywhere on the street, while in more developed countries you may have to find a taxi stand. Even if you can't read the words you can usually find the taxi stand just by looking at where the taxi's congregate. It is generally safer to get a taxi from either the hotel valet or from a taxi stand as usually only authorized taxi's are allowed to stop at these stands.
To flag down a taxi either wave your arm, or raise it slightly over 90-degrees from your body and motion with your hand and an empty taxi will pull over.
Many countries have fare systems similar to our own, where there is a meter on the dash that tallies the total cost. If there isn't a meter then I suggest you work out a price before you get in the cab. This will avoid haggling or being virtually forced to pay what the driver wants when you reach your destination. This is not uncommon in many countries. If a price cannot be negotiated on before getting in then don't take the cab.
Developed countries will always have meters in the taxi's and make sure the driver uses it. In third-world nations this can be more difficult, and sometimes you will have to go without the meter. If the taxi's have meters and the driver won't use it, you can bet you are getting charged almost double or more what the metered rate would be.
If the driver won't use the meter then make sure you negotiate the fare first, before the driver starts to drive. Foreign taxi drivers are not always out to rip off travelers, but it does happen.
Many cities have a set price, or extra surcharge when leaving the airport. You will usually see this posted on the airport taxi stand. Some airports have 'limousine taxis’. Basically these are a bit nicer cars, for a lot more money. They really aren’t worth the extra money and , unfortunately, you will many times people in the airport directing you to these over-priced options. Just keep your calm and walk past all the hucksters and look around where the public taxi stand is.
If coming and going to the airport, and you want to save money, then sharing a taxi can be a cheaper option. At the airport look at what the other tourists are doing and see if there are shared mini van taxis, also look for uniformed airport employees directing people to taxis.
If you are in a legitimate taxi then they will usually have some kind of a sign affixed to a window, the back of the front-seat or on the dashboard. The sign will usually have the taxi identification and a telephone number to call to report problems such as overcharging.
While these are a good way of identifying a legitimate taxi, unfortunately you will probably not get a refund if calling the number. It is usually just easier to pay and learn some travel wisdom then it is to bother and report fraud. However, you may want to write down the specifics so you can report it to your embassy when you get back home. There is a chance they may pass the complaint on to the tourist board of the foreign country which could end up helping other travelers in the future.