If you wish to see the Emrald Islands, you need to know the following additional information:-
If you are not a citizen of India, you need to declare your arrival at the airport and produce your travel documents.
If you are travelling around 15 August or 26 January, dont carry pins, batteries, liquids etc in your baggage.
Make alternative arrangements for stay at Kolkata/Chennai in case the flight does NOT take off or return without landing.This is more true during monsoon season. Port Blair airfield gets flooded when it pours heavily. If you are already at Port Blair, make arrangements there.
If you are visiting Baratang Island, you will have to cross Jarawa country.Clicking a single photo of Jarawas can land you in Jail. And it will NOT be the Cellular Jail. Anyway it requires clearance from the administration and hence stick to guided tour.
The Andaman group of inhabited islands are open for tourist stay except for certain specified islands reserved for the aboriginal tribes. Nicobar group is not open for tourism.
You will not be able to do much of snorkelling or recreational diving if you land up between April and November. The summer monsoon morphs into winter monsoon - wind direction changes. In a normal year one can expect 3200 mm of rain.
There is a bed and breakfast concept being introduced by the local tourism department. Since the logistics of sustaining the Islands are difficult, do not expect much in terms of local infrastructure - tourism is in its infancy here.
Do not litter the pristine beaches. Non bio degradable waste is a blasphemy to nature. Plucking Corals is the worst sin one could commit.
Do not expect fresh vegetables to be readily available. Try and stick to seafood - it maybe significantly cheaper. For a veggy meal try the Bay Island resort's Sunday Brunch. It is rewarding for its ambience, breathtaking view and a delicious spread.
Fishes die of old age. Fish and eat.