As stated above, the application process, including interviewing, is the same as it is in the States.
That said, except for non-hourly service positions, there is one crucial difference in getting hired and it has nothing to do with the process of applying and interviewing but everything to do with who you know. Simply, the weight given to an applicant with a personal connection to someone in the hiring organization (even indirectly) far outstrips the weight afforded to the best candidate for the job. There is even an expression in PR for this rule: "El que tiene padrino se bautiza."
Obviously, personal connections get people jobs in the States as well, but I have yet to meet a non-Puerto Rican who has sufficiently grasped the depth to which it is absolutely crucial to have a personal connection to get a job in PR. The reality is that it is very rare in PR that the best candidate for the job is hired.
One of the many aspects to the prevalence of this practice is the thinking that, "Why should I hire this guy when I can hire so-and-so's nephew, and then both of them will owe me a big favor in the future?" We would think that the profit motive would dictate that the best person for the job would be hired but, amazingly, we would be wrong. Unfortunately, extensive networking does not counter this regrettable cultural practice. This is one of the few aspects of Puerto Rican (and Latin American) culture that I have never been able to accept or grow even somewhat comfortable with.
The only exception to this tribalist hiring culture that I have seen is the very rare cases where you may be interviewed by a non-Puerto Rican North American or a Puerto Rican who has adopted the Anglo cultural practice of hiring based on merit due to their personal and professional experiences. Often Puerto Ricans who have served in the military or have worked in the States in the professions reject the custom of hiring so-and-so's nephew, but these people are few and far between.
I completely agree with GreggK that speaking (fluent) Spanish is essential to getting a professional job. The only exception I have seen to this rule is that I have known non-Spanish speakers who have interviewed for service positions like waiting tables and were hired because they applied at places that serve a lot of tourists.
Excluding doctors, I know only three North American professionals who have gotten hired by a firm in PR (four if you include myself) out of dozens if not hundreds of applicants. Three of these (including myself) first had to be licensed to practice as attorneys in PR either at the State or Federal level first, so having that license helped get hired. I also know two Argentinians who were able to get hired by a quasi-governmental body but that was due to the fact that they had valuable technical skills. 99% of non-Puerto Ricans that I have known in PR either came here because they work for the Feds or have their own businesses.
The sad fact is that this practice of tribal hiring hurts regularly Puerto Ricans the most and they are therefore the most vocal in condemning it. This has not changed anything though.
What are your skills? Unless you have some very unique and valuable skills, I would say it is virtually impossible to have a proper career in PR.
I don't like sounding like Debbie Downer but this is such an important issue with such devastating economic consequences that I feel obligated to write this.
One small suggestion I have is to have two resumes for each position: One in English and one in Spanish. Alternatively, if your resume is very light, just do one single bilingual resume. If possible, have names of prominent people in your field ready to drop during the interview. Good luck!