Fly cargo turboprops out of SJU. Definitely check out fortresses El Moro, San Cristobal and the night life around Old San Juan, they tend to have festivals practically every weekend for something or other.
Try to take the ferry over to Culebra and Vieques, postcard beaches and they have some great bioluminescent bays on the East Coast especially around those islands.
And of course you can't go to PR without visiting and hiking El Yunque, the rainforest. The Bacardi factory tour is supposed to be a must-see as well, but can't say I 've tried it myself.