Avoidance of insect bites
There are a number of insects that may be encountered whilst abroad, (mosquitoes, ticks, sand flies) which have the capability of transmitting a variety of serious illnesses (malaria, yellow fever, Japanese encephalitis). It can not be stressed highly enough that the avoidance of contracting such diseases starts with the prevention and avoidance of being bitten in the first place, read more (http://www.nathnac.org/travel/misc/travellers_mos.htm)
Food and water
One of the common health risks whilst travelling is associated with the consumption of contaminated food and drink.
Regrettably food poisoning is a very common complaint whilst travelling overseas. Even with diligent care symptoms may arise.
The advice on sun protection whilst travelling to hotter climates has been the subject of much advice.