Dehydration/Heatstroke: Both of these are pretty obvious and avoidable. And yet, when I was working for the Park Service, I saw more cases of heatstroke and or dehydration than anything else. Do not be one of the people that try to climb the mountain with an eight ounce bottle of water! Take lots of water, and wear sunscreen and a hat. Be aware that once you clear treeline, you will be exposed to the sun until you cross back down into the treeline at the end of the hike. My personal preference is to carry at least three liters of water in my pack; and depending on the season, sometimes four liters. Be aware that there are few water sources on the trail in late summer and early fall to filter water from.
Hypothermia: This is another obvious condition that, unfortunately, seems to affect a lot of potential climbers. I suggest that before you leave for your trip you consult the forecast for the region. I would also suggest that when you pick up your permit from the Forest Service, you talk to the Ranger about the current and planned conditions. Such information will allow you to be better informed and to have the right gear. Also keep in mind that if you are camping at Trail Camp, its elevation is right below 12,000 feet. Even during a hot summer day, the temperature at such an elevation can drop dramatically at night! It is also a good idea to have warm clothing for the final stage of the ascent as the temperature at 14,496 feet can be quite cold, and storms can come up quite fast.