Connections usually start from Trang or directly from Trang Airport.
Combined minibus and boat tickets can be booked from any Trang tourist information shop, prices are fixed. For 350 baht (Apr 2018) you can get a minibus to the nearest jetty and a longtail boat to the main pier at the village of Ko Muk including a taxi to your accommodation.
For 250 baht you can get the 11:00 minibus to the nearest jetty and aboard the only ferry, departing once a day. It's recommended to arrange accommodation and a pick-up from the Ko Muk pier, otherwise you'll have a 3-km walk or 50 baht motorbike taxi ride to get anywhere on arrival.
The return trip is easier and cheaper, with the same ferry departing at 07:40. With no booking fees or middleman it is possible to get the ferry for 50 baht and a minivan to Trang for 100 baht, although 200 baht is the more likely combined fare.
The arranged minibus + long boat transfers back from the island to the mainland take around one and a half hours and leave thrice a day at 08:00, 09:00, and 14:00, dropping you at Trang (fixed price based on time, 300-400 baht (Apr 2018)) or Trang Airport Trang (fixed price based on time, 400-500 baht (Apr 2018)).