One of the major problems faced by people when visiting Lahaul for the first time is altitude sickness. This is due to the high atmospheric pressure and less oxygen concentration in the air.
To get used to this, you can start working out lightly and increase your lung capacity by doing cardio workouts. When you do visit the valley, you should try to take breaks when climbing so that your body can get used to the changes in the atmosphere. Additionally, avoid consuming alcohol or smoking tobacco during the trip as these things tend to decrease respiratory drive.