You need a yellow-fever vaccination certificate to enter Ghana.
Visas are required by everyone except Ecowas (Economic Community of West African States) nationals. Visas upon arrival are rarely issued.
Though it's technically possible to pick up a visa upon arrival, they only get granted in rare cases so it is highly advisable you get one ahead of travelling. Single-entry three-month visas (US$60) and multiple-entry six-month visas (US$100) are standard. You can get a visa extension at the Immigration Office in Accra near the Sankara Interchange.
Most nationalities need a visa for onward travel throughout West Africa.
The embassy issues visas for three months (C146), usually in 24 hours. You need three photos and a yellow-fever certificate. Three-month tourist visas are also available at the border at Dakola, costing CFA94,000.
A three-month visa costs €50 and requires a hotel confirmation. See full list of requirements at www.snedai.com.
The embassy issues visas for one month on the same day. Alternatively, you can get a visa at the border at Aflao (CFA15,000), but it's only valid for seven days and you'll need to extend it in Lomé.