Here are a few things to consider and a few ways to ensure you don't end up spending the majority of your holiday vomiting in the hotel toilet.
Firstly you need to bear in mind that if you are heading somewhere very hot, then it is going to be particularly important that you drink a lot of water and that you keep yourself hydrated. You will lose a lot of fluids through perspiration otherwise and this can lead to your feeling dizzy and faint. It's also important to remember that alcohol is dehydrating, so if you are on holiday to party then you need to monitor your water intake even more closely.
However complicated the matter somewhat is the fact that the water abroad is often undrinkable for people who aren't used to it. Water in many European and Asian countries contains a high concentration of natural minerals and because we aren't used to that we can end up feeling very sick if we drink it. To avoid this problem, make sure you buy lots of bottled water in large quantities and keep this in your hotel room.
You also need to be aware of insects when you're on holiday. The danger here is not just nasty, itchy red marks, but also the chance of disease or infection. The solution is to choose a hotel with air conditioning so that you can keep the windows shut (particularly at night when they will be attracted to the light) and to use lots of insect repellent. You should also be weary of insects you don't recognize and stay away from long grass and other areas where they might be hiding. Of course it is crucial before going on holiday to get any necessary jabs such as hepatitis A & B when you travel to developing countries.
Jet lag can leave you feeling groggy and unable to enjoy the first few days of your trip if you don't handle it well. Remember that flying West to East will cause the most problems, so be ready to write off the first day for quiet and relaxed activities. When you arrive at the other end, make sure that you try to switch to their clock immediately which might mean staying awake for 48 hours. Though it will hurt, it will mean that when you go to bed you feel tired, and that you will be able to wake up the next morning with 8 hours of quality sleep.
The most obvious risk to your health on most holidays of course though is the sun and this means not only sun burn but also sun stroke. Make sure that you ease yourself in to the sun bathing and that you wear a strong sun block – remember that you can still tan wearing them but it will help to prevent you from burning. Remember as well that you need to replace your sun block a few times a day, and that you should invest in a waterproof product if you intend to spend lots of time in the pool or sea. It's also important to wear a hat to prevent sun stroke even if you aren't worried about burning, and to take regular breaks from the sun to get some shade.