Ko Jum has three main villages and is home to about 1500 permanent local residents. On the west side of the island are about 20 resorts which provide very simple bungalow accommodation.
Most travellers arrive via the ferries that connect Ko Lanta and Krabi, which charge about 350 baht (the same price as for the entire crossing, even though Ko Jum is at the half way point). The fare can be paid on board, but pre-booking is recommended as the ferry is often full. Tickets can be bought from travel agencies in Krabi or at the main ferry offices at the old pier on Thanon Khong Ka, and with resorts on Ko Jum.
Ko Jum has no jetty or dock - the ferry stops offshore and is met by longtail boats. If you've pre-booked, then a boat from your resort should be there to pick you up; otherwise simply choose one and ask for a lift to shore.
Ko Jum is a relatively small island and most of the population gets around on small 100-125cc motorbikes, which can be rented easily. There is also a local taxi service, comprising a motorbike and sidecar! The roads are narrow, unsealed, and frequently pot-holed and wet, and can be very challenging for inexperienced riders. Only in the main village is there a concrete road surface.
It seems unlikely that there are any problems on Ko Jum but take usual precautions.