Many Thais text/talk and drive. Just because everyone else is using their mobile phone doesn’t mean you should too. In fact that means you should be paying extra attention.
Speed is not well policed on the highways and is a major killer around Thailand. Don’t speed and don’t tailgate.
Sure no one else seems to use them, but indicating when changing lanes will increase the likelihood of others seeing and reacting to what you’re doing on the road.
Drink driving is common and not well policed. Don’t drink and drive, ever. Either have a designated driver if you are going out and will drink or hail one of the many cabs.
Seat belt usage is not well enforced. Shockingly many taxis don’t even have back seat belts. If you’re not in a rush and traveling long distances it might be worth letting belt-less taxis go on and waiting for one that has them. Always buckle up and use child seats for small children.
Cars on the road in Thailand often have more mileage. Regularly service your car and do a safety check before long drives. Take care to ensure tyre pressure is right before setting off.
When you can, avoid driving at night and in rain. It’s not always possible, but the number of accidents dramatically increases in Thailand at these times. If you do head out, drive carefully.