There are many approaches to traveling to Peru from the U.S. You can zip in for a long weekend and a short trip to the North Coast for surfing or to Machu Picchu for a mini-adventure, you can book a two week organized tour to see the archaeological sights and get a taste of a few more aspects of this remarkable country, or you can spend weeks or months exploring without ever running out of adventures. I always recommend spending at least two weeks there if you possibly can.
Traveling on your own in Peru is great if you have patience, a relaxed approach to travel, and interest in setting up and dealing with all the details. Things may not go exactly as planned, but that can be fine if you have the time and the right attitude. If you have a limited time frame you should limit your goals. If you would rather take a guided tour, look for a reputable organization that provides both a tour manager (to take care of logistics, make sure things do not go wrong, and fix them when they do) and an archaeologist or other expert (to provide up to date and accurate information of the kind you are most interested in). Although I am not endorsing or specifically recommending any of these, you may be able to find good tours through museums, university alumni associations, or Elder Hostel. There are also specialized companies that provide such things as running tours, which can be wonderful, although you may not get the same quality of cultural information that you can get from the more educationally focused organizations. Be aware that there are many, many guides (both credentialed and uncredentialed) in Peru and they vary tremendously in training, language skills, and accuracy and currency of the information they provide.
Considerations for planning a Peruvian itinerary
If you only have two weeks or less to spend in Peru, I recommend that you plan to spend a week in the Cuzco-Machu Picchu area (minimum of 5 days), a day or two in Lima, and the rest of the time in one of the other areas, such as the North Coast (Chiclayo-Trujillo area, where you can see some key sites in 2-3 days if necessary) the South Coast (Paracas-Ica-Nasca area, which is worth a longer stay but Nasca can be done as a day trip from Lima if you fly) or South Highlands (Lake Titicaca region, and/or Arequipa-Colca Canyon – either or both of these can be done as add-ons to a trip to Cusco without returning to Lima). These are not the only places worth seeing in Peru, by any means, but they each have enough tourist infrastructure to make it possible to get there relatively quickly, and get around while you are there. If you have a longer time in Peru, enjoy. No matter how long you are in Peru, make sure to try the pisco sours.