You can always ask at your hotel reception desk or concierge service for their recommendations of local tour operators. Once you find a tour operator you will be to choose the specific day trips or outings that most appeal to you.
Each tour company will more than likely have their own combinations of full day or half day tours that take in different attractions that can be found on the island. Obviously the prices of tours will vary depending on the tour and duration. However, you can normally expect to pay somewhere in the region of 900 to 1600 Baht, which will include transfer from you hotel.
Here is a taste of some of the things that you can expect to see and do on one of the many Koh Samui tours:
Elephant Trekking – Take a journey on an elephant through the islands jungle, visiting waterfalls, plants and exotic wildlife along the way.
Phang ka Snake Farm – Watch incredible snake shows and find out about the different types of snakes that are native to Koh Samui.