There is one traffic rule above all others that it really is best to obey all of the time: Keep to the correct side of the road. It's easier than you might think to get it wrong.
This is generally done by European or American tourist renting a motorcycle in Thailand. It unleashes a chilling primeval fear when you round a corner to find a huge one-ton pickup truck bearing down on you. So how to avoid this dangerous behavior?
Write a reminder on the headstock or on some tape stuck on the fuel tank. You're likely to see it when you insert your key. Starting off is the most likely time to forget which side you should be on.
Tie a piece of ribbon around the left-hand mirror so it's flapping just enough to remind you periodically to be on the correct side of the road. Stick tape with 'LEFT' on your right-hand mirror, as you're likely to be using this more when pulling away on the roads in Thailand.
Use the same idea of the tape on anywhere you're most likely to see regularly on the rented motorcycle, e.g. on your tank-bag, speedo, anywhere to keep you reminded..
Some people have used a wristband on their wrist, but I think you tend to get used to that and ignore it after a day or so. Many people also have their closest misses when they get back to Thailand from trips to Laos or Cambodia and forget to switch their mind-set back to 'the left' so be aware not to do that...