Snorkeling is a must. Although they say that the water off Puerto Rico is not the best in the Caribbean for snorkeling, I thought it was great. Then again, I''d never been snorkeling before, so perhaps experienced snorkelers would disagree.
Also, don''t stick to the typical restaurants that seem to be catering to tourists. Walk down a side street and find somewhere new.
A walk through Old San Juan is also necessary. Apparently not so safe at night, Old San Juan is beautiful during the day with its pastel-colored buildings and cobblestone streets.
And finally, buy some ice cream from a street vendor - it''s out of this world. Piña (pineapple) is my favorite, but coco (coconut) and parcha (passion fruit) are good too.
Quick Tips:
Be wary, just as you would be anywhere. I had heard how dangerous Puerto Rico was, but upon arriving I realized that it''s just like anywhere else. Use common sense - don''t wear flashy jewelry or watches, don't carry a lot of money around, don't look like a typical tourist reading your guidebook.
It's wise to stick a Spanish phrasebook in your bag because not everyone speaks English. Usually you can get along fine with broken English mixed with a few words of Spanish, but a phrase book couldn't hurt. (I was travelling with a fluent Spanish speaker, which was even better!)
An hour or two before sunset (around 5pm) is a great time to go the beach. The crowds have gone, the sun isn't as glaring, and the locals come out to relax for a while after work.
Best Way To Get Around:
Walking is fine for getting most places, especially if just around Condado or Old San Juan. The bus is a great way to get in and out of Old San Juan for .25 each way, provided you get on the correct one and can find the bus stop - ask the front desk at your hotel which bus you should take.
Old San Juan also has a free trolley that takes you all around the city - it begins at the bus terminal. If you must take a taxi, negotiate the price before you get in. A car is not necessary unless you plan to travel very far outside of San Juan.