Add a free day - I find the best days on a trip to be those where you have the time to breathe and reflect on your experiences. Do not underestimate the value of a free day, this might end up being the favorite day of your trip.
Don’t skip Lima - Lima is worth a visit! Enjoy the incredible cuisine, walk along the Pacific Ocean and learn more about the history of Peru. There is more to Peru than just the Inca culture and Machu Picchu.
Pack light - There is no need to bring half your closet with you on your trip. Most restaurants, museums, etc. in South America have a relaxed atmosphere, and a formal dress code is rarely required. Prioritize comfortable clothes you can layer for different temperatures during the day and evening.