The best way to reach Ko Jum is through a ferry that departs from Klong Jilad Pier in Krabi. Krabi is also the nearest airport to Ko Jum. From the airport, you can public as well as private transport to reach the ferry pier where you can get the tickets to the ferry as well. Once the ferry drops you off, it heads on straight to Koh Lanta.
However, please note that this ferry operates only between the months of November to April. During the other times, you would have to hire the Longtail Boat to reach your destination.
Ko Jum is a very small island and visitors can either walk short distances or can commute from one place to another on motorbikes, sidecars and cycles. The roads on this island are quite well-constructed and visitors can easily move on them. Car and bike rentals on the island and they can also be pre-booked online on Expedia or Travelocity. Bicycles are more convenient since they can be easily rented, are cheap and can be taken anywhere on the island, even on the beaches! Bicycles can be rented at cycle shops on the island itself or online.