Sorry vs Thank YouThose who are new to Japanese language tend to overuse the word arigatou (thank you). If you listen to the way Japanese people speak — arigatou isn't all that common a word.
In Japanese language, it's common to say sorry when English speakers would say thank you. For example, if someone holds a door for you — English speakers tend to say thank you. In Japan, it's more common to say sumimasen (sorry) in this situation.
If you use arigatou to thank a stranger for a small favor, people will understand what you mean. However, it doesn't always sound completely natural.
It's two different ways of looking at the same situation. You can be thankful that someone helped you or feel sorry for having inconvenienced them. In Japan, the later thinking is far more common.
Casual ApologySumimasen is the most common way to make a casual apology to a stranger. For example, if you bump into someone its common to say sumimasen.
If you want your apology to seem more sincere try bowing a little. It's also common to hold your hand in front of you when making such an apology.
Formal ApologySumimasen deshita (sorry for what I did) is the most common way to make a formal apology.
Let's say you get caught skipping work to go fishing. This is the way to apologize to your boss.
Gomensai is another common way to apologize. However, it's used to apologize to someone you with whom you have a close relationship. For example, you might apologize to your boyfriend or girlfriend with gomensai. It's a little too personal to use on your boss.
RestaurantsIn Japan, waiters and waitresses don't usually come to your table unless you call them over.
If you need something you're expected to summon staff by saying sumimasen. In fact you can yell it if you need to.
Asking DirectionsIf you plan to ask a stranger a question — sumimasen is the way to start. In this context it means excuse me.
Sumimasen is ranked #1 of 10 most important Japanese words for travelers