What are the main things I should know before coming to Japan?

When you use escalater, you should stand on the left side and keep the left for the people in rash. But this rule works in Tokyo and it becomes opposite in Osaka (the left side is for people in rash).

Learn few Japanese words :) Like "Thank you" is "Arigato", and "excuse me" is "Sumimasen". That would make a lot easier to interact with local Japanese!