Indonesia has a Visa on Arrival (VOA) policy for issuing a 30-day tourist visa. In 2009, all that is necessary to get one of these is to have a passport with six months remaining validity, and then submit the application form with two passport photos and $25 upon arrival. For most visitors to Bali, this will take place at Ngurah Rai Interational Airport in Denpasar. Otherwise, you are entering Bali by means of a domestic, Indonesian sea ferry and have already acquired a VOA somewhere else.
An important consideration for all visitors to Bali, but especially for those who are going to be heavily active outdoors, is the sun. Bali is only 8 degrees south of the equator, making its sunshine equatorial rather than merely tropical. It is extremely strong, and standing in full Balinese sunshine is akin to being in a microwave. Do not expect your sunblock to be as effective as advertised, so bring along the strongest sunblock you can find, as well as a good sun hat and some loose clothing that covers a lot of skin for when you are not on the beach.
Also remember that the climate in Bali is usually hot and always humid, so expect to drink a lot of water to stay hydrated. Treated water in Bali should be viewed as suspect, so always drink bottled water or treat the water yourself using either iodine or chlorine, combined with a carbon filter.
Malaria is only a minor problem on Bali, and then only in the backcountry highlands. Dengue and other mosquito-borne diseases, however, are found in Bali. The best approach to disease prevention is to get your basic shots brought up to date before going to Bali. The Centers for Disease Control recommends rabies and typhoid shots in particular for those spending time in rural areas, as hikers and mountain bikers must necessarily do. Past that, bring a bottle of deep woods mosquito spray and apply it vigilantly. American bug repellents are permitted to have much higher concentrations of DEET than those in Bali, so it pays to pick up a bottle before leaving.
Picking a Beach
If you are going to Bali, it is a given that you will spend at least some time on a beach, and there are plenty to choose from. Kuta beach is a good place to learn how to surf, while Nusa Dua has waves that are often 12 feet high and is better for more experienced surfers. Snorkelers will find dolphins and easily reached reefs off the black sand beach at Lovina, on the north coast. Scuba divers will probably prefer to locate at Tulamben Bay, on the east coast of the island. The area has good dive sites literally right off the beach, including a ship wreck, and access by boat to all the other dive sites near Bali.