Whilst we cannot vouch for all their advice or practises, Blevins Franks, have a long and respected reputation for financial advice, tax, BREXIT and the Spanish legal maze.
They offer books, videos and free basic guides to paying taxes in Spain. They often advertise free seminars in the area where you can meet and quiz their experts in relaxed surroundings.
Use the link below to find an array of published guides (PDFs) and books. e.g. Franks & Blevin, AIPP, etc
https://www.blevinsfranks.com/download/tax-guides/
