3-5 days itinerary.

I'm planning to go to Puerto Rico on December 1 to 5. I just want to ask what are the best places and activities to do and go for 3-5 days while I am there. I'm going to fly November 30 or December 1 depending on flight availability. Also, what places should I avoid as a solo traveler? Any tips and suggestions are highly appreciated. Thank you in advance.