There are several ways to reach Koh Tao...

The easiest way is flying to Bangkok and then take the domestic flight to Koh Samui. With Bankok Airways you reach Koh Samui in about 50 minutes. From Koh Samui, take a boat to Koh Tao. The trip with Lomprahya takes aprox. 90 min.

Another way is to fly to Phuket and minibuss or taxi to SuratThani and then speedboat (Lomprayah).
You can also take a bus from Bangkok to Chumpon. This bus trip takes about six hours. From Chumpon, take an hour trip by boat to Koh Tao.

If you prefer to travel by train, this will take a longer time to Koh Tao but on the other hand you can book a sleeping-van to Chumpon and then the boat to Koh Tao.

We recommend Lomprayah catamaran boat before any other boats, from Koh Samui or Chumpon.