Working in Ghana is not as different to European or American standards as one might think, at least not in big companies. Of course there are some country specific things you should know.
Ghanaians tend to get up early, so the usual working hours are from 8am until 5pm with a minimum break of 30 minutes. The maximum hours of work per week are 40. Generally there is a provision for overtime and at least 15 days of paid holidays have to be granted by a company each year. The country has 12 public holidays. If one falls on a weekend the day off will be transferred to the upcoming Monday.
As in Western business environments you should dress smartly and be polite. Ghanaians usually address people by their title (e.g. doctor) and greet people by shaking hands from right to left when entering a room.
In most situations a little small talk is expected. Exchanging business cards is quite common. You should receive them with your right hand and in general do things with the right hand as the left hand is considered dirty. Many companies have a casual Friday, where workers come in traditional and/or casual dresses. Inform yourself beforehand to avoid an unpleasant surprise.