You arrive at Ban Pei Pier and there are hundreds of speed boats to choose from. My suggestion is to insist on the White Shark boats. The charge (return) is B1000 - no matter how many are on the trip with you - so if you're alone, try to group up with some other travelers. Try not to go on public holidays/long weekends. The accomodation will probably be fully-booked (that's if you haven't booked ahead of time), and the beaches are pretty crowded. There is no ATM on the island, so make sure you have enough money with you - most accomodation and restaurants have machines where you can swipe your ATM card through.
There is no accessible transport on the island as the roads are dirt, so take care when hiring one of the off-road clutch bikes they have on hire for around B400 a day. Expensive but it's all there is.
A massage is about B400 for two hours and the BEST meals are to be had on Ao Pudsa Beach, at Charlie and Nu's restaurant - best you try the Indian Curry they have there. YUMMY!!!!!!