Useful Japanese grammar book
If you’re struggling a bit with Japanese then there are a couple of great bibles of Japanese grammar which you should check out.
Written in cooperation with the Japan Times, the Dictionaries of Japanese Grammar are a complete source of well informed and written guides to grammar points.
There are hundreds of cross referenced entries as well as useful appendices and indexes. Although the explanation can be a little technical at times it is precise and well written in English with various examples in Japanese and English so you can see what and how to use the grammar.
They are also quite compact and sturdy so if you fancy whipping it out on the train to bone up on the way to that JLPT test you won’t have a problem.