Studying abroad in Japan

I always suggest extremely targeted study towards what you expect to do while you are in Japan.  I would skip the textbooks and memorize the kanji for the place names you plan on visiting.  Go through a few phrase books and memorize anything that seems like you need to use while you are there.  Learn some useful phrases for ordering food and learn to spot your favorite dishes on a menu printed in a weird kanji font or hand-drawn(search japanese menus and practice reading them).  There is some good practical stuff on this website.  Most stores (convenience, grocery, etc) will not have english labels on products, so prepare in advance by knowing how to read labels of some products you think you might need.  Knowing the names of condiments and ingredients is helpful.  A funny example from the first time I went to japan was when I bought a doughnut expecting jelly inside, it is quite a shock when it's curry instead!  Know how the trains work and the difference between super-express and local and know how to tell which train stops at which station.  If you will have a smartphone with international data, learn to use one of the train schedule apps.

But also be realistic about how much you can learn before you get there.  3 Months isn't very much time unless you are studying full-time and even then it's not enough time to learn anything beyond basic conversation.