See the Stay safe section of the Scuba diving article for diving safety tips. Be aware that the islands are closed from mid-May to Early November of each year. Tour operators going to the islands during the closed times are not only risking your your comfort but safety.
fees/permits
The National Park fee is 400 baht/day children 100 baht. For Thai citizens the fee is 40 baht, children 20 baht.
Diving fee is an additional 200 baht/day regardless of passport.