Taxis in Glasgow are mostly pretty reasonable but can be extortionate after midnight. One thing to be wary of is boundary charges. The greater Glasgow area is covered by a number of local authorities and each of these issue taxi licences. This is why taxis from the airport can be so expensive as they cross a boundary to get into the city centre.
Unique Suggestions: Ask the driver how much it should be, they should be able to give you an idea before you set off.
Fun Alternatives: The buses in Glasgow are pretty reasonable so it is much more economical to buy a day ticket for the bus or bus and underground together.
If you are staying outside glasgow city bounderies try and book a private hire taxi (you will find numbers in phone boxes or just ask someone) as the black hackneys (london cabs) will charge a boundry charge, and this can add an extra third to the price and private hire only charge for the distance traveled.