As a city in a Buddhist country, Siem Reap follows strict etiquette when it comes to anything associated with religion. In theory, visitors here should avoid pointing their feet directly at another person or from wearing short sleeves or revealing clothing in a religious building.
Cambodian greetings are customary among locals but not necessarily a faux-pas if performed incorrectly, as long as someone else's greeting is not ignored. If you want to get in with the locals, hold your palms together in front of your chest in a sort of praying motion upon meeting someone followed by a handshake if that other person is a man.
Perhaps the most important, and most difficult, local custom to follow is not to show any anger. You may have just been charged 10 times over the odds for a tuk-tuk ride 500 metres around the corner but to get angry means a massive loss of face for yourself and the driver. Feel free to put across your point of view, but do so without swearing or raising your voice and everything should work out much better.
There isn't too much that can go wrong when eating out in Siem Reap. Make sure to never get angry with any of the staff to preserve face and fully expect for animals, babies or just about anyone or anything to share the restaurant space with you. This is no reason for complaint in Cambodia.
When paying the bill, make sure to check whether the currency you are planning to use is readily accepted. Leave a tip at your own discretion. In a low-cost restaurant serving Cambodian food you would not be expected to leave a tip, although you may do so; while in a mid- to top-level place, 10 per cent would be considered fair.