Diana,
I have been living in Japan for about a year now, and came to Japan on vacation twice before I moved here to teach English. Big difference between vacationing in Japan and living/working in Japan. A vacation to Japan is a lot of fun - expect culture shock as it is very different here from anything you have seen in the Western world.
However, a word of caution, as you are a female, when riding the very, very crowded trains it is entirely possible that you will be groped by Japanese men. While the stereotype of Japanese men as being reserved is true for some, many act very differently towards gaijins. I have heard many female English teachers that have confirmed this has happened to them when riding the trains. Also, the trains while very convenient are over-priced and very confusing to first-time visitors. So, get a map of the train system the first day of your arrival - they have an English version.
Also, though Japanese study English in high school, most can not speak more than a few words and can understand virtually no spoken English. Furthermore, they generally consider it rude that gaijins ask questions in English. So, don't expect much help - better to find your own way, if possible. If you are travelling in Tokyo or Osaka, the Japanese are very familiar with foreigners, but in rural areas this is not true. Someone wrote that Japanese do not make much eye contact, but they will stare at you relentlessly if they find you interesting to look at! Haha...
I am not sure what your ethnicity is, but if you appear "Latin" or "Spanish-looking" expect more staring. The Japanese are used to seeing a lot of white Americans or Canadians, but are generally less familiar with Latin, Spanish or Latinos, though there are quite a few Brazillians in Japan.
You will find that many Japanese are very polite, but understand that this is their culture, it doesn't necessarily mean that they like you. Like most things in Japan, it is just for show.
On the plus side, Japan has an abundant supply of very beautiful women...but guess this won't interest you much!