From Bangkok : Fly to Koh Samui airport with Bangkok Airways or Thai Arirways. At the airport after you collect your luggage. (Be carful if you're on "Hot Transfert" from Int. to Bkk it's not sure that your luggage will follow, give our adress to the lost items department and your belonging should arrive in 24h in front of your doorstep.)
Find the Lomprayah ferry office there is a ferry leaving the pier at 12h30 ( make sure you get to Koh Samui airport for 11.00), the ferry company will organize your transfert to the pier, you will be on Koh Tao around 14h15, our staff will be welcoming you on the pontoon.
Relax you just arrived in your concealed paradise.
Tips: Treat yourself in the ferry go up to the 1st deck and get a VIP seat for 100 Thb