Taxis are still reasonably cheap in Greece. Count a cost
of about 1.20 Euro per km out of town, a little less
in town. Make sure that the meter is set or arrange the price beforehand.
If you take a taxi at major taxi stands, you will often see a price table listing the costs of a drive to the main destinations.
There is a small surcharge from airport and port terminals, as well as on some holidays (Christmas, Easter).
You can also stop a taxi anywhere or order one by phone (small surcharge).
Phone numbers vary so check locally.
It is not unusual for a taxi to stop even if it already has a passenger. If you are heading in the same direction they will take you. Generally this does not mean a saving for the passenger but two fares for the driver. Don't begrudge them this small extra profit, with the low cost of taxi rides taxi drivers don't earn that much.
Tipping is optional and not taken for granted. Most taxi drivers will speak at least a little bit of English.
Be careful when specifying your destination: many places in Crete have similar or similar sounding names and misunderstandings can occur quite easily, especially when this is compounded by poor pronunciation of Greek names. If in doubt, show your destination on a map.