Currency: The Guinean franc (GNF). Guinea is a cash economy. There are a handful of ATMs in Conakry (Ecobank, Societe Generale), but they are unreliable and often empty. Outside the capital, ATMs are essentially nonexistent. Bring euros or US dollars in cash and exchange at banks or informal money changers. Credit cards are not accepted anywhere outside a few top-end hotels in Conakry.
Language: French is the official language and is spoken in cities and by educated Guineans. In rural areas, local languages dominate -- Fulani (Pular) in the Fouta Djallon, Malinke in the east, and Susu along the coast. English is rarely spoken. Even basic French will make your trip significantly easier.
Visas: Most nationalities need a visa. Guinea offers an e-visa system -- apply online before travel. You will need a valid yellow fever vaccination certificate, a passport valid for at least six months, and a passport photo. Visas are typically valid for 30 days.
Health: Malaria is endemic throughout Guinea. Take prophylaxis and use mosquito nets. Yellow fever vaccination is mandatory for entry. Tap water is not safe to drink -- use bottled or treated water. Healthcare facilities are extremely limited; carry a well-stocked first aid kit and consider evacuation insurance. The 2014 Ebola outbreak hit Guinea hard, but the country has been Ebola-free since then.
Safety: Guinea is generally safe for travelers in terms of violent crime against tourists, but petty crime (pickpocketing, bag snatching) is common in Conakry, especially around markets. Political demonstrations can turn violent with little warning -- avoid large gatherings. Road checkpoints are frequent; always carry your passport and visa. Travel after dark outside cities is not recommended.
Electricity: 220V, 50Hz. Plug types C and F (European two-pin). Power cuts are frequent everywhere, including Conakry. A headlamp or torch is essential.
Internet: Mobile data is available in cities via Orange or MTN SIM cards, which are cheap and easy to buy. Coverage outside major towns is patchy to nonexistent. Wi-Fi exists in some hotels in Conakry but is slow.
Tipping: Not expected but appreciated. In restaurants, rounding up is sufficient. Guides and drivers should be tipped.