Most of the advice given above is good. The best (although sometimes impractical, depending on your schedule) way to reduce the risk of AMS (acute mountain sickness) is graded ascent- a night or two in Denver first will help your acclimatization. Breck has the problem of being situated at a higher base altitude than most of the CO resorts (about 1300' higher than Vail, for example), so you run a somewhat greater risk there. That being said, many people have no problem at all- there are genetic factors at play, and you may be lucky! If you have had problems with AMS before you should consider graded ascent and perhaps prophylaxis (drug treatment) more seriously.
Several things that will help- and several that won't:
1. there is some evidence (not conclusive, but persuasive) that a high carbohydrate diet begun at least 3 days prior to ascent may be helpful.
2. drinking plenty of fluids WILL help with the problem of dehydration (which is considerable at altitude, for multiple reasons), but has NOT been shown to retard the development of AMS. You certainly should play close attention to adequate hydration, and dehydration can mimic the symptoms of AMS. Indeed, if you have a headache and vague nausea, drink a liter or more of fluids and see if you feel better. If not, be much more wary of how you feel- you may be developing AMS.
3. Take it easy on your first day- avoid over-exertion for at least 24 hours.
4. The issue of alcohol and altitude is complex. There is a long-standing adage that alcohol has more potent effects at altitude, but that appears to be a myth. There is some evidence that it may slow your speed of acclimitization, however. Also, be wary of dehydration- alcohol may cause this. This is also the only real problem with caffeine. If you are strongly affected by the increased urination (diuresis) from caffeine keep a close eye on your fluid intake. Otherwise, there is probably no reason to avoid caffeine.
5. prophylaxis- the use of acetazolamide (Diamox) has been proven in many studies to accelerate the acclimitization process (at least 75% effective). Lower doses than recommended in the past appear to be as effective in most people- 125mg twice a day. Side effects include tingling of the fingers and toes, increased urination (got to watch for dehydration again!), and it imparts an unpleasant taste to carbonated beverages. People with sulfa allergies cannot take this drug (the chemical structures are related). It is available by prescription only, and should be started 24 hours before ascent. A new approach that has not been completely validated, but has some preliminary positive results is the use of ginko biloba (120 mg twice a day, beginning 4 days before ascent).
6. DON'T SMOKE! If you do, stop at least one week prior to ascent. Smokers have high levels of carboxyhemoglobin (essentially carbon monoxide poisoning), and you will need every bit of hemoglobin you have to carry the little oxygen that is in the air up here. The constrictive effects of nicotine onthe blood vessels is not good either, but nicotine patches are preferable to smoking. A related issue is that if you are anemic, get treated before you ascend, so your oxygen-carrying capacity will be optimized (benefits of iron will take a few weeks).
7 I almost forgot- although exercise and fitness will help you perform better, it actually does little or nothing to reduce your risk of AMS.
If you really get sick, see a doctor (there's a clinic right at Breck). The optimal treatment of AMS is DESCENT. Even descending 1000ft (that is about the level at Dillon or Silverthorne) may be effective.
Have fun and pray for more snow! Even though it has been alot warmer than usual, it was great at A-Basin yesterday! And don't forget your sunscreen.
(note to Ant- many asthmatics actually do better at altitude. The lower density of the air may be a benefit (less resistance to flow in the airways). Also, albuterol, which most asthmatics use as a first-line treatment when they wheeze, has been shown in a very well conducted study to be very effective in helping to treat HAPE (high altitude pulmonary edema, the lung disorder that can occur at high altitude)