Have a look at the Spain Buying Guide, http://www.spainbuyingguide.com, it has lots of useful information about renting.
I have been renting in Spain for 6 years after selling my property & am very happy with my situation. The important things is to understand the contract you will sign, your responsibilities and those of the landlord. I believe it is always a good idea to rent before you buy anyway, so as to get a feel for an area & to see if it suits you. If like me, you choose to rent permanently, make enquiries about your landlord before you sign anything. Mine is very good, punctual with repairs and correct but this isn’t always the case. Anyway, I wish you well with your plans.