Learn a Bit of Spanish
Despite the island's official affiliation with the United States, Spanish is still the most widely spoken language. While most people speak English in the more touristic regions of the island, you may expect to find many areas where this is not the case.
It's also crucial to be aware that the English language has the potential to instill emotions of fear and inferiority in some elder generations who don't speak English well or at all. Learning some basic Spanish before visiting Puerto Rico can not only make things easier for you, but it will also show respect for the locals.
While there are many English speakers in the touristy areas of Puerto Rico, the more off-the-beaten-path areas are entirely Spanish-speaking. As a result, learning a little Spanish ahead of time will make your trip much easier and more fun.
Not to mention the fact that you tried would be appreciated by the locals. Even if you have no intention of learning Spanish before you arrive, attempt to pick up a few popular words or phrases.