Overall, Ghana is very friendly, and food and drink is inexpensive - outside the Western hotels.
On arrival at the airport, bear in mind that Ghanaian culture does not approve of "calling out". If the customs inspectors want to attract your attention they will "hiss" at at you, a kind "ssssssstt!" sound while extending an arm in your direction. This is the generally approved way of attracting the attention of a waiter in a bar or restaurant, and you might find "young ladies" will hiss at you, particularly in the vicinity of nightclubs, or hotel bars.
English is almost universally spoken - primary education is conducted in English - and handshaking is almost de rigeur. If you go to a large assembly such as a wedding reception you are likely to be met by somebody who will take you to shake hands with all the important people in turn. At a business meeting you should shake hands with everybody present on arrival. Some ethnic groups conclude a hand-shake with a "finger-snap" - snap your middle finger against the thumb. Observe who is doing finger-snaps and who isn't and seek to emulate - the fact that you are trying to fit in is more important than getting it exactly right.
There are about seven significant dialects spoken in Ghana, though several of them are variants of Twi. In Accra, Twi is supplanting Ga as the dominant language, and in Eastern region Ewe predominates. "Akwaaba" means "Welcome", "E te se" or "E te de" means "How are you" - to which the response is "Me hooeeAy". Some people may say "Bo Kor" (these are phonetic spellings) to which the response is "E ye". "Paa" is an emphasizer meaning "very" or "very good". "Paa" is very versatile, I have heard whole conversations where every other word seems to be "paa".
One peculiar construct of Ghanaian English is "Is this for you?", which means "Is this yours?" but is a direct translation of the Twi grammatical construct. There are few gendered words in Twi, so "he" and "she", "his" and "hers", "husband" and "wife" often get confused in Ghanaian spoken English. "Mrs Thatcher ruled his cabinet with an iron fist" might be satirical to an Englishman, in Ghanaian English it is a direct translation of Twi without recognizing the distinction between "his" and "hers". "He is his wife" makes perfect sense to a Ghanaian, but the "proper English" could be "She is his wife" or "He is her husband".
If you find the Ghanaian word for "please" do let me know. The nearest cognate is "M'pacho" which literally means "I beg you" and is not used as frequently as we would say "please". This does not take away from Ghanaian politeness, they will smile broadly, and just appear a bit direct. Thank-you is "Me d'aase", which means something like "I commend you to God".
If you are shocked by penises, don't go. Whether it is small boys getting bathed in a bowl by the road side, or men "paying the water rates", you will see many male members.
Be patient. Ghanaians are polite, and eager to be of service, but they do not understand urgency, or a Western obsession with haste. If you annoy a Ghanaian official (s)he will take extraordinary care over their duties.