1 Do not be aggressive - The Japanese are inherently "shy" when it comes to strangers. Japanese society is very rigid and follows the strict social traditions based on honor, pride and respect. Trying too hard to continue to Japanese friends who are not interested in you will never work. In fact, the best way to defeat the Japanese slowly over time, so it does not appear simply interested in sex or "showing off" type of relationship. In other words, do not ask for phone numbers for the first time to meet someone!
2 We're not talking about the Anime / Manga - Contrary to popular belief, most Japanese people are addicted to anime or manga. In fact, the word "otaku", which refers to someone who is worrying is dependent on the medium (the hentai) is derogatory in Japan. If you are "Otaku" type of person, you will probably scare away most reasonable Japanese people. They will probably think you're creepy.
3 Do not try to be Japanese - Also contrary to popular belief, not to "impress" Japanese girls or boys, knowing a lot of Japanese words and Kanji symbols. They can pretend to be impressed, but mostly they will think you're creepy, yet again. Knowing everything about Japanese history and the J-pop singers and movie only will you look like a weirdo for most Japanese. Remember, the Japanese are interested in foreign cultures, so that they remain a stranger! Learning fluent Japanese will only waste time and break your heart. (In fact, most people secretly hate foreigners or Japanese "gaijins" to "move" in Japan too long ... love visitors, or english penpals, but they hate each other "wannabe" ninjas .)
4 They have a purpose for sex - Japanese people, even those who are interested in a great party or in English, still prefer to have some sort of order to their relationships. If those who study abroad in America, for example, guys can help each other with a movable or errands, or practice English together, or have fun together if both do not have many other friends, etc. This kind of friendship where there is mutual benefit, has long term potential, even when a Japanese friend returning home. However, after the departure of Japanese just because they are "interested in their culture" does not sit well with Japanese people.
5 Find Japanese who are internationally oriented - Believe it or not, even though Japan is super modern country, many Japanese prefer to keep to myself. They buy Japanese products, watch Japanese television shows (generally), and wish the Japanese spouses and friends. That's what they know and trust. However, things are slowly changing, and there are many Japanese who have become very interested in learning English, working or living in other countries, even from non-Japanese people. These are usually Japanese men who have been more outgoing, or "abnormal" in their own country. Therefore, these types of Japanese may be too flirty, silly or crazy ... but at least are interested in you!