There is one main road running north to south on the island that connects Sairee, Mae Haad, and Chalok, with many smaller roads branching off from it. Some roads lead over the spine of small mountains that run along the middle of the island and are all dirt, can become impassable after rain, and can be challenging even to a skilled driver. If you are looking for an adventure, the dirt roads are a good place to find it. Also be aware that distances can be quite deceiving due to the quality and elevation changes of the trail. As of October 2016 many of the roads are actively being replaced with freshly poured concrete, though this has led to an increase in speeding compared to the older worn down/dirt roads. The other main thoroughfare is a pedestrian pathway known locally as the "Brick Road" (or "Yellow Brick Road" despite being gray) that runs along the majority of Sairee Beach from Mae Haad to the main intersection of Sairee. Despite being a pedestrian path there's still numerous scooters weaving and bobbing, so be sure to keep an eye out.
You can rent bicycles and motorcycles at many places around the island, though there's an increasing number of rental shops are running motorbike scams where they hold your passport hostage and insist on you paying large amounts of money for non-existent scratches upon their return — primarily shops on/near the "Up Road" from the Mae Haad pier or near the Sairee 7/11. Make sure you note and photograph all scratches and dents when you take delivery of a rental bike, including the underside of the bike as it inevitably will take a few bumps once off the main road (if the shop is charging less than 200 baht/day for a 125cc scooter, chances are they're making up the difference elsewhere). Taking passports as the deposit is standard even at reputable shops, though some will alternatively take a deposit of 8000-10000 baht for a typical 125cc scooter if you ask.
Some of the hostels also have motorbikes for rent.
ATVs have been recently banned from the island, though may still be seen roaming the island once or twice during your stay. There are usually plenty of taxis available in both Sairee Village and Mae Haad, however they tend to be expensive for Thailand with a minimum price of 300 baht or 100 baht/person when transporting larger crowds. Longtail boats offer rides to and from hard-to-get-to beaches on the island. They are a more comfortable way of getting to isolated beaches than attempting to ride over the mountains, however they are noisy. A round-island longtail can be as much as 2,000 baht, whereas some short trips will only be 100-200 baht.