Currently, the US State Department advises you to reconsider travel due to terrorism, piracy, civil unrest, and kidnapping. If you are going to visit family or are a Nigerian citizen, you’re likely more strongly motivated to go. In that case, steer clear of the most dangerous territories.
If you are a tourist who wants to go to Nigeria anyway, your best bet is to stick to well-traveled areas. Stay off back roads, take tours if you’re going somewhere more remote, and stay indoors at night.