Slower Pace. It's island time! A major part of the charm of Puerto Rico is how relaxed and friendly the people are. Don't forget that when you're in a line somewhere and it's moving slow, this just comes with the territory. Expect things to tick a bit longer and do what the locals do with the extra time; talk to those around you and be more approachable!
Irregular Hours/Schedule. Banks are open from 9am to 3:30 pm - usually. Other businesses can have hours that vary and might change with little or no notice. The larger chains from the states, like Walmart or Burger King, will be reliable.
Possibility of Bugs. Just like any area around the world or even in the USA, there are also bed bugs in Puerto Rico. Usually bugs, mosquitoes and sand fleas are worse if you’re near a body of water, like in the rivers. Whereas if you’re located somewhere in upper elevations, there’s typically not much of a problem like that.
Windows. They have bars on windows. Perhaps it can be a cultural thing or just a typical Puerto Rican style to have these kinds of windows. It may feel better to know that there are bars in the windows--or else, it will just be like an open hole. It can also be useful like good for hanging your washed clothing for them to dry.
Still Some Damage After Maria. Hurricane Maria was devastating to the island. As of the time of this writing, everything is up and running except on the mountains. They prioritize places of businesses, places most people would go to. Some articles claim that people should not visit Puerto Rico because it takes the resources away from the locals, well, that might be true after the few first weeks after the hurricane, but that’s ridiculous now. The best thing you can do for the island is to go there and spend money to help them rebuild their livelihood. People are happy to see you, you’re not taking food or water out of other people’s mouths. You’re putting money in their economy.
As you drive the island, you’ll see some damage here and there on the mountains, El Yunque got hit pretty hard, so definitely before you go places, if you’re going to put a lot of energy into going somewhere, make sure they’re open; most places have opened up as of this time of writing. It’s always good to check.
The rainy season stretches from April to November, so if you want to visit the island, it’s good to know that there might be chances of hurricanes to show up during that time and it may rain more. Though during rainy season, it’s very rare that it rains all day long. It rains for a few hours, in the evening maybe. It doesn’t rain daily either. At least not very long. It’s not a bad time to travel, but you just need to know that there’s a risk for hurricanes. You can plan it out, and when it’s time to go, there’s a big hurricane and it may mess up your plans. It’s always good to be ready.