Leave yourself a day or so to recover from travels at each destination.  Flights to Lima from the US often arrive late at night.  Also, altitude sickness WILL be a factor in Cuzco.  We came from 7,000 feet in Colorado Springs to 11,000 feet in Cuzco, and WE had altitude sickness.  So don't try to book tours starting the minute after you check into the hotel.

Be patient with air flights within the country.  Planes depart for all destinations many times a day.  You may get bumped from a flight, but the next one will only be an hour later.  Think of it as waiting for a city bus.  Check your itinerary frequently before entering Peru to keep up with the "dynamic" state of air travel in Peru.

Most places we visited in Peru accept dollars almost more readily than Nuevo Soles.  Keep lots of small US bills on hand--sometimes a store won't even have change for a five dollar bill.  Make sure your US money is in good condition--no tears or missing corners.  ATM's are everywhere.  Lima even has Bell Atlantic telephone booths.  As with all foreign travel, it's always a good idea to have some of the local currency for when you can't use dollars (i.e. Taxi rides, local markets, travel outside of major cities).

Be prepared to eat lots of steak or Italian food.  While the Peruvian national specialty is potatoes (the Spanish got them in Peru and introduced them in Europe), most restaurants serve either steak or pasta.  You can find local cafes that serve chicken as another option.

Check the weather before you go.  The weather is always changing in Peru.  And travel from Lima to the Andes to the rainforest takes you through many climates.  You can check out the weather at:  Peru Weather (Weather Courtesy of weather.com)