Dress modestly – it’s a sign of respect in the local culture; cover your shoulders and knees when going to places of religious significance.
Try to wear white to the religious sites – white in Buddhism is a color of purity.
Be respectful to Buddha – don’t wear any clothes with his image.
Don’t express intimate affection in public – Sri Lanka is quite conservative, and any expression of affection beyond hand-holding is frowned upon.
Eat like the locals – in the same places and always with the right hand, while using your left hand for cleaning.
Keep calm – don’t raise your voice or engage in arguments.
Answer any questions locals might have for you politely – and there will be a lot of those questions, Sri Lankans are very curious about other cultures!
If you can, avoid talking about Sri Lankan politics and the recent civil war – it’s a sensitive subject.