Well, I've never been to Peru but if you're planning any excursions to the mountains I can tell you as one who suffered horribly from altitude sickness in the Himalayas to go and have a chat with your GP before you leave. Ask his advice on this most debilitating condition, and just in case he's the type who doesn't know much about this subject, have a search on the internet. And if you start feeling ill, descend as soon as possible - a long period of oxygen starvation can have very serious consequences, including damaged vision and even a risk of a stroke.
Apart from that, enjoy the trip.