First of all, rent a car or jeep! This will allow you to visit many beaches, historic landmarks and trails that you might ordinarily miss if just taking taxis. There are quite a few jeep rental companies in downtown Cruz Bay.
Be sure you have enough gas in the tank. You don't want to run out of gas when you are all the way on the East End of the island where there is no gas station. Both gas stations are located in Cruz Bay. Gas is expensive so be prepared. Gas is about $1.00 more than most stateside prices. The speed limit is a maximum of 35mph. But within Cruz Bay it is 20mph.
Remember that you will be driving on the left. Although this is a remnant from Danish rule, we say that you drive on the left so that you can see how close you are to the edge of the road and the steep slopes below! Sitting in the passenger seat becomes a whole new experience so be prepared for some comments on your driving. It is frightening to see a huge safari bus coming right at you.
St. John roads are very serpentine and steep in some places. Just take it nice and slow and you will be fine.
Be sure to visit the following places on your tour, this could take anywhere from a couple of hours up to a full day depending on how much time you spend at each location.
Start in Cruz Bay (where you can rent your vehicle for the day or longer). Take Route 20 East.
First Stop: Mongoose Junction
This is still in Cruz Bay but if you haven't been there to shop you will want to visit there before moving onto the next stop. You'll find some really unique shops with local arts and crafts and exotic imported merchandise. Two shops we really like are the Caravan Gallery and the Best of Both Worlds. There is a deli and restaurants if you want to grab a bite to eat.
Second Stop: Caneel Bay Resort
This was once the home of Laurance Rockefeller who donated most of the land that he owned to the National Park system in 1956, keeping the Caneel Bay property for himself. Thanks to him the island of St. John has remained largely unspoiled and undeveloped. Caneel Bay Resort has a nice beach, a good beachside restaurant (not cheap) and beautiful grounds. If its not too early stop there and have one of their Plantation Punches made with local rums, fruit juices with a splash of Meyers Rum on top and a dash of nutmeg.