The Japanese language is written using two phonetic alphabets, known as Kana and Hiragana, and one ideographic alphabet known as Kanji. There are also several ways to write the Japanese language using the Roman alphabet. These methods are known as Romaji. The most popular Romaji system is the modified-Hepburn system. The one chosen by the Japanese government, Kunrei-shiki, is so stupid that it doesn't warrant comment.
Japanese teachers generally start by teaching Romaji, followed by Hiragana, then Katakana, then Kanji. Better teachers will skip Romaji. There are many problems with this method of teaching. It is essential that students learn Kanji from the very first lesson, so that Kanji cease to be seen as a difficult hurdle, something to be tackled at some point in the distant future. The very reason that Kanji are difficult is that they are not taught from the outset. A student learns to recognize various Japanese words, learns their meaning, and learns their pronunciation. These three aspects become one item in memory. A year or two later the student is introduced to the Kanji characters for these words. It is very difficult to add a Kanji character to something that has already been memorised.
Only two people told me to learn some Kanji characters before moving to Japan, Mark Rebuck and Ben Jones. Mark sold me a huge number of Japanese language textbooks for a pitifully small amount of money, books which are still useful to me today, six years later.
For those wishing to visit Japan, the most useful thing to do is learn some Kanji characters. The best book to use for this purpose is called "Read Japanese Today" by Len Walsh, published by Tuttle. My copy has "Mark Rebuck, 1992" written in the front cover.