A few suggestions to make your stay safer, easier and more comfortable.
Regardless of the season and the area your are visiting, it is advisable to carry warm clothes, loose pants, cotton tops, hiking footwear, good sunblock and a hat (to protect you from the sun and the cold).
Don't let your personal belongings out of your sight.
Avoid using unofficial or unmarked taxis during the night.
Avoid exchanging currency in the street or carrying large sums of money. Currency exchange agencies are safe.
In case of altitude sickness, rest well during the first days avoiding physical strain; drink mate with coca leaves or take coca pills.
Drink plenty of fluids, particularly in high altitude zones, using only bottled or previously treated water.
Purchase your food at restaurants, avoiding street food.
Peru's electricity runs on 220 volts and 60 cycles (except for Arequipa where it is 50 cycles)
There is no preestablished amount for gratuities, it depends on the customer's level of satisfaction with the service. 10% of the check is usually considered adequate.