Fly to Koh Samui (then a short ferry), or fly to Surat Thani and take a bus-and-ferry combination (cheaper). Direct ferries also run from Koh Samui and Koh Tao.
From Pattaya
Route via Bangkok to Samui or Surat Thani. It is an overnight-or-longer trip.
Getting around
Songthaews, taxis and scooter rental; some northern beaches need a boat or 4x4.