You should show integrity and professional sympathy. This means you can display persistence in your negotiations as long as you ensure the atmosphere is relaxed and friendly. The ideal person should be able to gain introductions and be in good standing with potential business partners and the authorities. You need someone with status. It matters to have graduated from the right university, to live at the right address, even to drive the right car.
Time advances slowly in Spain.
This is even truer for the public services than it is for business. When you work out a schedule for the negotiations and the implementation of a transaction, allow for the time it will take if you need to apply for licences. Do not enter contract negotiations in the belief that everything will proceed as it might in your home country. Be prepared for the unexpected delay. You should visit the offices of your counterpart between 9.30am and 1pm or between 4pm and 7pm.