Language
Bahasa Malaysia (Malay) is the national language, but English is widely spoken, especially in cities and tourist areas. You can get by with English almost everywhere. Chinese dialects (Mandarin, Hokkien, Cantonese) and Tamil are also common. In Borneo, dozens of indigenous languages are spoken alongside Malay and English.
Currency
The Malaysian ringgit (RM/MYR) is the currency. ATMs are everywhere in cities and towns. Credit cards are widely accepted in hotels, restaurants and shopping malls, though hawker stalls and small shops deal in cash. Money changers in city centers typically offer better rates than banks or airports.
Safety
Malaysia is generally safe for travelers. Petty theft and bag-snatching occur in cities -- keep valuables secure in KL especially. Drug trafficking carries the death penalty, and this is enforced. The east coast of Sabah near the Philippine border has had security concerns in the past; check current advisories before visiting remote islands in that area.
Health
No vaccinations are officially required for most visitors, but hepatitis A, typhoid and tetanus boosters are recommended. Dengue fever is present throughout the country -- use mosquito repellent, especially during the wet season. Tap water is treated but most people drink bottled or filtered water. Medical facilities in KL, Penang and other cities are excellent and much cheaper than in Western countries -- Malaysia is a popular medical tourism destination.
Religion and customs
Malaysia is a Muslim-majority country, though Chinese Malaysians are predominantly Buddhist or Taoist and Indian Malaysians are mostly Hindu. Mosques are everywhere and the call to prayer is part of daily life. Dress modestly when visiting mosques and temples -- cover your shoulders and knees, and remove shoes. During Ramadan, eating and drinking in public during daylight hours is discouraged in conservative areas, particularly on the east coast.
Alcohol is available in non-Muslim restaurants, bars, supermarkets and convenience stores, but it is taxed heavily and more expensive than in neighboring countries. A beer in a bar typically costs RM15-25.
Electricity
230V with British-style three-pin plugs. Adapters are cheap and widely available.
Time zone
Malaysia is GMT+8, the same as Singapore and Hong Kong.
Connectivity
Mobile data is cheap and coverage is good. Pick up a prepaid SIM at the airport -- Hotlink, Digi or Celcom are the main providers, and a tourist SIM with several GB of data costs around RM30. WiFi is widely available in hotels, cafes and restaurants.
Tipping
Tipping is not expected in Malaysia. A 10% service charge is added at most restaurants. Rounding up a taxi fare or leaving small change is appreciated but not obligatory.