Given below are a few suggestions as to how to prevent Altitude Mountain Sickness (AMS).
1) Avoid smoking, caffeine, Alcohol during the Annapurna base camp trek. In fact start cutting down on caffeine from at least a week before the base camp trek so that you don't have any withdrawal headaches during the trek.
2) Drink at least 4 litres of water a day while on the trek. You dehydrate faster than you realize and symptoms of dehydration are similar to AMS. So do make sure you are fully hydrated so that you can rule dehydration when the symptoms like headache starts appearing
3) Take it slow: There is no need to rush during the trek. Everest and its base camp are not moving anywhere :) There is anyway not much to do at the tea house so take your time and reach the tea house only by evening. If you feel your heartbeat is rising from too much walking, stop, take deep breath, relax and once you recover you can start again at a slower pace
4) Plan itinerary of the trek with acclimatization days: Most of the people that fail to do the trek till base camp of Everest, fail only because they covered too much too fast and didn't plan for acclimatization days. 2 rest days at Namche and at Periche or Dingboche are recommended. On your rest days go for short hikes and ask your guide to take you to higher altitude than where you will be sleeping on the next day. Spend some time at that altitude and come back.
5) Take Diamox: Use Diamox when you get headache and continue it till the time you don't descend to a lower altitude than where you started it. It means, if you started taking it in Periche, take it regularly till the time you come back to Periche again or continue it even beyond till you reach a lower altitude.
6) Avoid sleeping tablets: At high altitudes you might have trouble sleeping but don't use sleeping tablets. Sedatives reduce the flow of blood to your brain and in high altitudes where there is already less oxygen in your blood, it could have severe consequences.
7) Don't carry heavy weights: You are already physically strained with the challenges posed by high altitude of the base camp trail and don't test your limits by carrying too much weight. Use the services of a porter. Try not to carry more than 5-8 Kilos by yourself
8) Don't trek alone: Altitude sickness can include panic and crazy behaviour and you must have someone by your side to pay attention and help you. Typically, AMS symptoms get worse in the night. If symptoms of AMS get worse, make sure your guide or friend accompanies you till you reach safer altitude or medical help arrives.
9) Never ignore or leave alone anybody who shows signs of AMS. The conditions could deteriorate much faster than you imagine and it may be necessary to arrange a helicopter rescue.
10) Dress warmly and prevent your body from cooling. Make sure your clothes are always dry.