Visitors should take the necessary precautions against insect bites. Use DEET-based mosquito repellent and wear long pants at night. The northern coast has one of the highest incidences of Dengue Fever transmission in Peru and malaria can also be passed along through mosquito bites. That said, few travelers have any problems with either disease so long as they heed the above recommendations. 
Also, take sun protection especially seriously on the north coast of Peru. The sun is strong, and if you are not careful, it can burn you quickly. Your skin is most vulnerable in the middle of the day, so stay out of the sun in the early afternoon.
The northern coast does not require any safety precautions above those normally taken while traveling in Peru. Never wear expensive jewelry or flash around large sums of money. If you need to carry cash and important documents, carry them in a money belt against your skin.