Before I went I was told to go where lots of tourists go, only be out during daylight, and when the cruise ships reboard, go inside and stay there. It's worth the trip but be cautious. Drugs are hidden in plain sight but there is safety in numbers and in daylight, together.
"only be out during daylight"
Sorry but that is absolute nonsense. There is a very active nightlife on St Thomas enjoyed by both travelers and locals. The safety rules on island are pretty much the same as every place else: avoid dark alleys, don't go looking for drugs, and use common sense.