How do I book a taxi ride in Spain?

It is not clear where are you takin the taxi from, so I'll assume it will be directly from the airport.

1. If you google "taxi malaga" you will find some companies offering their services. Note that some are not offering metered taxis but actually rent a car with driver services (taxis must offer the stablished fares)¹.

2. That said, if you arrive at the airport I would expect taxis to be available at the taxi stop unless you arrive really early or late. Check your destination to confirm that.

3. Taxi licences are based in a municipality (town), and fares too (so a taxi fare may vary from town to town). Also, taxis are barred from serving in other towns; if you pick a taxi in Malaga it can give you a ride to Marbella, but a Malaga taxi cannot pick you in Marbella unless you have booked it expressly to ride you to Malaga. Which is a justification for having to pay the return trip to your taxi if they ride you to another town, even if it goes empty.

4. Take into account that picking a taxi and going to another town means that you will have to pay for the taxi to ride back to its town, even if it is not used (as the taxi driver cannot pick anyone in town Y).

5. Legally they cannot refuse you entry, but there is always the taxi driver who refuses to obey the law.

   That said, you have to look terrible for the taxi driver to refuse a 100km drive. Also, if you have booked the taxi and they refuse you entry, they would lose not only the money for the drive but also the time they spent waiting for you.

   I would say it could be more of an issue (if at all) for picking up taxis once you are at your destination.

6. Tipping is not mandatory but appreciated.

Malaga airport has a web (only in Spanish, of course!) and gives a list of approximate costs for reaching several of the nearby towns. Note that "Tarifa 1" is working days between 06:00 and 22:00 and "Tarifa 2" is the rest of the week. Note that for a metered taxi the "valid" cost will be the one metered by the taxi, the fares listed in the page are orientative.

As one of the comments said above, calling your destination about the alternatives could give you more detailed info (if there are alternative transportation means, if there is a need to book or if it is better to book at your destination or at the airport, etc.). If there are no better alternatives, you are not going to stay long and you are comfortable with driving in unknown roads, I would consider the option of renting a car.

¹I have never used one of those so I cannot say which are their pros and cons.

It would help if you were to name the resort you are going to.

Malaga airport has a taxi rank that operates 24 hours a day. You will be able to take a metered taxi. The cost would be high. Ronda which is just over 110 km away would cost approximately 150 euros as detailed on the Malaga airport website mentioned in another answer

http://www.malagaairport.eu/es/servicio-de-taxis.php

It might be cheaper to prebook a shared shuttle bus service. There are many different ones, and ones that I am aware offer services from Malaga airport include www.holidaystaxis.com and www.hoppa.com. There are many others and I offer no opinion on the reliability of any,those are the two I have used from that airport.

Malaga airport is on the main costal train line, and it might be possible to save money by taking a train from that station, to a closer town, and then onward taxi. Again the destination you are visiting would help so we can offer ideas.

A tip in a taxi is normal, but not compulsory, approx 10%. But your journey is quite long so 10 euros would be acceptable. For short journeys, I would round up to the nearest whole euro.

Malaga is a holiday and cosmopolitan town, and sees holidaymakers from around the world, so you should have no issues based on your background, however all Licenced Spanish taxis have a complaints book. And if you have problems you can request to write a complaint in the book, which is reviewed by the licencing authorities