with your Japanese class/textbook. I'm using the Minna II book and keep having to look up various grammar points. I started looking around the grammar bank on this website, and have since started kicking myself for not fully using this site.
The easiest way is to look up via the romaji pulldown menu for whatever grammar point. I usually save each page as a PDF (I use a Mac so it's extremely easy), and also print out when I'm not near my computer.
The added bonus is that Jpod101 lists each episode where you can find this grammar point!!! Some of the ones I'm currently learning are in the intermediate sections. I would have never thought to listen to those because I'm not there yet.