DON'T use slang or profanity.
DO note that people who live in the south of Nigeria speak louder and more directly.
DO be aware that in the southwest of Nigeria, where the Yoruba tribe resides, they use a lot of proverbs and humor throughout conversation.
DO understand that Nigerians communicate with a lot of gestures and body language, so you may have to pay attention to non-verbal cues when conversing.
DON'T make generalizations about religion in Nigeria. Nigeria is a religiously diverse country, so it's important to understand that and maintain an open mind.