As the island is large, you cannot see it on foot or cycle. Some people choose scooters. But, unless you are already a good rider, it can be dangerous. You should try to find a scooter rental shop that doesn’t require your passport as a deposit. And, if you ride one, always place your belongings in a backpack and keep it strapped onto your chest. Never place valuables in the front basket as this would be inviting thieves and pickpockets to rob you. Ride slowly to avoid potholes. It is best not to ride your scooter in the rain. Always wear your helmet and never take more than one passenger.
If scooters are not your thing, you can choose Songthaews. These Thai ‘taxis’ are not metered. You’ll need to negotiate the rate with the driver. You can team up with fellow travellers to pay less.
Long-tail boats are good for seeing places that are hard to reach.