No special BVI rules... well, since the majority of charterers really don't know the rules, I consider myself the "give way" vessel all the time unless given clear indication by the other boat that they are giving way. This applies not only to other sailboats but particularly to big powerboats including ferries.
The system used in the BVI is IALA-B (red-right-returning) and anchoring is prohibited in coral, national park moorings cannot be used for overnight stays. Overboard discharge of grey and black water is not enforced and I've heard that many holding-tank equipped charter boats have the valves wired to "overboard discharge".
The markings on the map are not necessarily what you get. Sometimes markers drift away and are not replaced in a timely manner. The only place this might be worrisome is when entering or leaving the Anegada channel as itis shallow and narrow.
I can only think of 2 cardinal markers, one at the Trellis Bay entrance and another around the SE end of Beef Island (very close inshore). The guide books and charts
clearly mark the very few danger areas. Most charter company chart briefings go into more detail about bars and restaurant than navigational hazards because the area is quite easy to sail.
I head down to the BVI early next week. What sort of a boat are you chartering and for how long?
You'll love the BVI, once you switch to Island Time it'll be "no worries, mon".