Do not go out alone on Friday night as many people will be drunk and dangerous.
If you wish to go swimming make sure you go with locals who know where they're going. While snorkelling on the reefs is beautiful, some have resident sharks and or crocodiles. The locals know which ones to avoid. Also be aware of strong tides and currents.
Dengue fever occasionally occurs, but shouldn't be much of a problem there has only been one death in Australia due to dengue in the last 50 years. Just make sure you use insect repellent. Malaria rarely occurs on the islands closest to PNG.Be aware of the tropical climate. It can get very hot and muggy so wear loose clothing and drink lots of water.
respect
Make sure you are very respectful of Islander culture by not going to ceremonies without invitation.
talk
There are two main indigenous languages in the islands: Meriam Mer in the Eastern islands, and Kala Lagaw Ya in the rest. Most people also speak Brokan, which is in many respects similar to Tok Pisin spoken in Papua New Guinea. Most people also speak English, although with much slang not found in general Australian English.
Learning a few words of Brokan will make you quite popular with the locals.
Thank you = Esso
Food = kaikai
Goodbye = Yawo