How to apply for Spanish nationality

"¡Que viva España!"

How I did it:

1. I had in order all the papers of my grandparents and my father.
2. I got my birth certificate reprinted at the _Registro Civil_ (Civil Registry) and then I got an apostille.
3. I filled out the required forms.
4. I submitted them at the local consulate, along with my passport. You can also set an appointment directly on their website.
5. They sent me an appointment at the Embassy in Mexico City.
6. I showed up for my appointment to sign two or three more papers. 
7. They told me they'd get back to me in a few months, as they're very busy with the overload of applications they currently have. 
8. Now I'm waiting for my nationality certificate. 

Lessons & tips:

• Make sure you have all the required original documents.
• Bring copies of all documents. They keep only the copies except for your original birth certificate with the apostille.
• My grandfather's and father's birth certificate was particularly helpful to have. Those were the only papers (copies) that were needed in my case, but it gave me peace of mind that I had _all_ the other papers with me.

Resources: Solicitud Nacionalidad Española
This webpage has all the information and links to the forms you need. It also allows you to set an appointment at the Embassy.

It took me 5 months.

It made me very fortunate

See more progress on: apply for Spanish nationality