From the point of view of a westerner living in Nepal, I'd agree with everything suggested so far, but there's a few I find very obvious that ALWAYS seem to be missed:
Read the road: You should, at all times, know what every vehicle within at least 100 meters ahead of you is doing at all times, and, be prepared for them to do the stupidest thing possible, because, in south Asia, that's probably what they will do.
Keep your distance: In the UK we call this the 3 second rule, you should always be 3 seconds behind the vehicle infront of you, this is especially important with larger vehicles like lorries and busses, especially at highway speeds- remember, if you can't see their mirrors, they can't see you!
Never, ever, ever overtake on the left hand side: Over taking bikes it's not a big deal, we can see equally well to the left and right, but anything else, car, micro, bus, lorry etc, they have a drivers seat on the right hand side of the vehicle, this means seeing what is happening on the left is no-where near as easy. In the UK we call this undertaking, not overtaking, it's an offence, is considered dangerous driving, and repeatedly doing it can lead to losing your licence.
Only use your horn when you need it: Over using your horn makes it meaningless, if you're one of those who has his/her thumb constantly bouncing off the horn button, chances are, no-one else is listening anymore, it just becomes background noise, when you need to use it to avoid an accident, no-one else will actually notice it. If you only use it when you need it, it will stand out, it will catch people's attention.
Make your passenger wear a helmet: I know it's not always possible to carry a second helmet, but when you do have the option, use it. The passenger is more likely to fall off and injure themselves than the driver, and trust me, you don't want that on your conscience for life. Don't worry about what's "cool" or "stylish". I recently saw two boys spending a good 5 minutes discussing how they could carry a second helmet on their scooter as it was too big to fit under the seat. I sat there, on my bike, saying "put it on your head" repeatedly. They looked at me as if I was insane as they continued to discuss how they could carry it comfortably. In the end, I picked it up, put it on the passengers head and said "this is how a helmet works".
Never back-seat drive: A back-seat driver is a passenger who spends the whole journey advising the driver instead of letting the driver drive. I had a friend of a friend on my bike recently, he was in the same age bracket as my friend's parents, and the most dangerous passenger I've ever had. First he sat there at the first junction saying "pull out, pull out now" as large vehicles like buses and lorries were coming towards us. I said "No, because I don't want to die". Chances are, if there is a bus or lorry, there is a taxi or bike trying to overtake it that you can't see, quick way to crash! Once I'd finally pulled out at a safe moment, while I was on a strait road, he reached forwards and started adjusting my mirrors! I'm VERY picky about my mirrors, they're the first thing I check when I get on a bike/in a car, I need to be able to see behind me, not only that, but they're attached to the blooming handlebars! So while he was adjusting my mirror to show me a delightful view of my shirt, he also nearly caused us to crash. I quickly barked "KE GAREKO?" at him, in a voice I use only for badly behaved students, before I put my mirror back where it was. I was ready to stop the bike and make him walk, I could have punched him I was so angry, and trust me, it takes A LOT to make me angry, but putting my life in danger, that's near the top of the list of things that work.
Make sure ALL your lights work: I drove a car on the highway at night a while back, near Bhutwal. I have never been so scared. I learned to drive in Wales, which has roads more or less exactly like the highway roads in Nepal if you consider the width and regular bends, we drive on those roads at 60mph (about 98kmph) day and night, and it's safe, because everyone else drives sensibly. But the biggest risk here wasn't the bends, it wasn't the holes from the road not being maintained, it was the sheer number of lorries, tractors and busses that didn't have working lights. You see one light coming towads you and thing it's a bike, it gets close and it's a lorry with one headlight broken. Or before you know it you're hard on the breaks because you're behind a slow moving tractor with no tail lights. It doesn't only matter if you can see, it matters if other people can see you.
There's probably plenty more I could think of, and I may have repeated other people, but these things I didn't see on the lists other people posted as I scanned through. Good to see people here starting to think about road safety. It's a shame this group only represents a minority of people in Nepal.
Nepal has some of the most beautiful roads (the highways) I've ever seen, but you can't enjoy them because you're too busy stressing about the insane idiots you share the road with. If everyone drove safely, and the government bothered to maintain the roads, this would be one of the best driving countries in the world.
Lets talk about safe ride