完全マスター is a good way to マスター the grammar. If you take a picture of your copy, you can ask for a premade spreadsheet
here containing all the sentences, so you can review them using
Anki.
If you're not already using Anki or smart.fm or something, then that's another thing you should start. Find a vocabulary list for 2級 and add all the words to a deck. You'll probably be able to find some premade ones somewhere. Remember to have example sentences somewhere on your flashcards so you're not just relying on J-E definitions.
I don't really know what to recommend for kanji, since it depends how you've been learning them. Personally, I used
Remembering the Kanji ages ago, and continue to learn readings from the vocabulary cards I mentioned above.
Other than that, you need to read and listen to whatever you can. Find some shows and podcasts you like, and maybe some approachable bunko if kanji isn't a problem. If it is, you could try one of the 2級 reading comprehension workbooks. 完全マスター has one. I find them pretty good, since you need to learn how to answer the kind of questions they give you on the test.
There's also more advice in these two threads:
http://forum.koohii.com/viewtopic.php?id=3504
http://forum.koohii.com/viewtopic.php?id=5385