Rather than worrying about infectious diseases or rickety airplanes, the bigger danger is road safety abroad - in other words, be careful with driving, yours and everyone else's.
According to the US State Department, fully a third of all American deaths overseas are due to road accidents so it's no wonder the United Nations decided to call 2011 to 2020 the Decade of Action for Road Safety. Bus fatalities are especially perverse, since this is often the preferred form of transportation for budget travelers.
That doesn't really help travelers, at least not until things improve. If we don't travel by road then how on earth are we supposed to get from A to B?
There are plenty of reasons why all these deaths and injuries occur:
If there's one rule I would observe, it's this: whenever possible, stay off the roads at night.
Not likely, especially if you're in places road transport is all you've got. There are a few ways you can stay sane and improve your safety chances.
A healthy dose of good luck helps, but so does common sense. If you're doing the driving, you'll research whatever rules exist before you leave home, and rent a car from a reputable company (try to aim for a sturdy model). It's easy to find out about reputations online these days, and the same goes for bus companies. Some simply have more accidents, so they're the ones you'll avoid.
If you're a pedestrian look both ways, especially if driving is on the other side of what you're used to. Haven't you ever been pulled out of the way of an oncoming bus as you crossed the street? And don't jaywalk. In Switzerland people almost get killed daily because traffic is so regulated that single lanes looping behind you get the green light so cars arrive from invisible directions just as you're convinced the street is utterly empty.
Planning on driving something on two wheels? Fine, if you know what you're doing, but don't use your trip as an opportunity to learn. If helmets aren't compulsory for everyone else, they should be for you. So should be something reflective or very bright on your clothing (in case of bad weather - because you won't be driving at night, will you...).
What are local attitudes towards women drivers? Whether the norm is to try to drive you off the road or give you a wide berth, it's information you should have.
Oh yes, and make sure you check if you need an international drivers' licence - you don't want to have to part with a fine each time you're stopped.
Here's hoping this never happens because getting into trouble in a foreign land is not good news.
This is where knowing local usage comes in very handy. In Algeria years ago I was warned never to stop if I ever hit someone while driving (fortunately I never had to test this particular piece of advice). The family would try to punish the driver, I was told, and punishment could go as far as lynching. Imagine not knowing that.
In some countries you'll have to call a special number, in others just ask someone to fetch a police officer. Either way you need to know what to do.
In any case make sure you get in touch with your embassy if you're involved in an accident or confronted with police, because if you're in serious trouble they'll be the only ones willing to help you. You certainly won't be able to rely on local authorities.
Sometimes you really can't help it. Your only choice from one city to the next may be a disreputable company and unless you want to backtrack, you'll take your chances, and most times you'll be fine - and a bit more aware.
And then there are those Alpine passes wide enough only for one vehicle, the newly-tarmacked surfaces of Sumatra, the tiny streets of historic Italy... Each time I prepare to ride a dodgy vehicle or climb a hair-raising road, I am petrified. While that doesn't stop me, I do take the train or fly whenever I can.