Important Tip when Docking:
St. Thomas has two cruise ports - - The West India Company Dock (almost universally referred to as Havensight) and Crown Bay. Both are located on the south side of the island not far from Charlotte Amalie. I've walked to town from WICO/ Havensight - taken a taxi from Crown Bay. Havensight has a Budget & Avis car rental just steps away from the ship.
A photo ID is required to get back into the port area!
Because Charlotte Amalie is basically in the middle, walk to your left from Havensight if you want to go to Havensight Mall in town - streets and streets of shops plus a decent little tented flea market with vendors who will haggle. (There is a small shopping area right off the pier but go to town for mega shopping!) Both Senor Frogs and The Smoking Rooster great bars/bbq to hang at on the pier. The skyride to Paradise Point is right near the pier and worth the gondola ride up to see an overview of the island.
Any beach on St. Thomas is great in my opinion but I favor Magen's Bay.
Water Taxi / Ferry to St. John's: Two places to catch the ferry - steps from the cruise ship on pier in Charlotte Amalie or take a taxi to Red Hook to catch the ferry. (Factor in the price of the taxi when planning) Found the Ship's "St John's On Your Own" excursion to be cheaper in the long run. Once off ferry, take a taxi to Trunk Bay for best beach on the island providing the sea is not rough. IF ROUGH, go to Caneel Beach or Cinnamon Beach - something closer to ferry - the ferry crew will tell you ocean conditions)