We advise you to consider the following recommendations
Do not eat heavy food the day before traveling to Cusco.
Make sure you drink between 6-8 glasses of water the days before your trip and during your stay in Cusco.
Once you arrive at your hotel, lie down and get some rest before going out to explore the city.
Drink coca tea; most hotels offer it for free at the reception of their facilities. Another option is to buy lemon candies.
Once you are ready to go out and explore the city, try not to become agitated climbing stairs or walking fast. The best thing is to go slow until you are fully acclimatized so you can enjoy your trip.