Samoa is a malaria free zone. However, there are occasional outbreaks of Dengue Fever and so precautions should be taken such as using mosquito nets and insect repellent. Note that the mosquito that transmits dengue normally bites during the day.
Drink bottled water. It's cheap and readily available.
There are no known poisonous animals or insects on land, although centipedes can give you a very painful bite. In the water beware of purple cone shells, sea urchins, fire coral, etc. If not using fins, wearing footwear while snorkelling is highly recommended.
Some travellers have reported a violent allergic reaction with the ceremonial drink kava. Symptoms include a very obvious rash and swelling to the neck and face area, sweating and discomfort. Medical attention should be sought immediately and a prescription for Prednisolone usually does the trick. It takes from 12-24 hours for the effects to noticeably subside.
There are two hospitals in Apia and one on Savaii at Tuasivi, a couple of miles north of the ferry wharf at Salelologa.
Samoa has an adequate telephone system with international calling. Some villages have public phones available and require a pre-paid phone card.
Samoa.ws, ipasifika.net and Lesamoa are the Internet Service Providers. There are several public Internet access points in Apia, where fast, reliable access can be had for around 12 tala 4 US dollars per hour. There are a couple of internet cafes on Savaii. If planning to stay in remote parts of Upolu or Savaii and you cannot survive without your daily internet fix then check in advance with the hotel to make sure it has wifi. Most don't.
The CSL cafe across the road from McDonalds in Apia has a fast internet connection for around 5 tala per 30 min. You can also buy credit there 15 tala for 1 h / 70 tala for 10 h to use your laptop at wifi lavaspots at various locations around town and even on Savaii (http://www.csl.ws/lavaspot.cfm) The lavaspot connection and download speed is very good. Some Hotels sell the same WiFi credit at higher prices than at CSL!
Samoa is very religious, with most of the population following one of the Christian denominations. This means that Sunday is generally respected as a holy day and most shops and businesses are closed. You should not walk through villages on Sundays.
Many villages have a prayer curfew in place at sundown. This normally lasts around half an hour. You should be careful to avoid walking through villages at this time to avoid causing offence.
Samoan culture is governed by strict protocols and etiquette. Although allowances are made for foreigners, it is wise to avoid revealing clothing and to comply with village rules which are enforced by the village matai chiefs, although Apia is quite relaxed in these traditions.
Women going topless is taboo, and they should only wear swimwear at the beach. Shorts should be knee length. Shirts should be worn when not at the beach. A lavalava sarong is nearly always acceptable attire.
Other simple things, such as removing shoes before entering a house or, for that matter, budget accommodation, should be observed.
The main island of Upolu is known as the "modern" island, where most northern coast villages are quite relaxed with the old strict traditions, whilst Savai'i is the more traditional island, but has become more relaxed. But nude bathing is definitely taboo.